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THE INTERNAL 
COMBUSTION ENGINE 



BOOKS BY THE SAME AUTHOR 



A PRIMER OF THE INTERNAL COM- 
BUSTION ENGINE. (Constable & Co.) 
Price 2s. 6d. 

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TRANSPORT. (Constable & Co.) Price 
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The Internal 
Combustion Engine 

A Text-Book for the Use 
of Students and Engineers 



i. E. WIMPERIS, M.A., M.I.E.E. 







FORMERLY SCHOLAR OF GONVILLE AND CAIUS COLLEGE, CAMBRIDGE J ASSOCIATE 
MEMBER OF THE INSTITUTION OF CIVIL ENGINEERS) MEMBER OF THE 
ENGINEERING STANDARDS COMMITTEE J THE R.A.C. EXPERT 
AND TECHNICAL COMMITTEE J THE GASEOUS EXPLO- 
SIONS committee; WHITWORTH SCHOLAR 



NEW AND REVISED EDITION 



NEW YORK 

D. VAN NOSTRAND COMPANY 

25 PARK PLACE 

1915 



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3 



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EXTRACT FROM PREFACE TO FIRST 

EDITION 

The present book deals with subjects in the borderland be- 
tween several allied sciences (notably physics and chemistry) 
and the exclusively practical sides of their application. It is 
hoped that the student will be helped to understand some- 
thing of the applications of those heat engines which work 
on the internal combustion principle, and the engineer to a 
fuller realization of the scientific principles concerned in the 
design and working of gas, oil and petrol engines. In order 
to economize space, and since it has been amply dealt with 
by many other writers, little is said of the historical side of 
the subject. The introduction, into the theoretical treatment 
of the subject, of the principle of the now recognized variability 
of specific heats with temperature has involved the breaking 
of much new ground, and it is impossible to expect complete 
success in avoiding mistakes and slips in the calculations. I 
shall therefore be very glad to have brought to my notice any 
corrections that may be necessary. 

In writing this book so many original papers and treatises 
have had to be consulted that it is not easy to make the 
requisite and proper acknowledgments. First, however, it 
is a pleasure to acknowledge my great indebtedness to 
Professor Perry, to whom, as a student many years ago, 
and on numerous occasions since, my thanks are due for 
guidance, counsel and help generously given. I have also to 
thank Mr. Dugalcl Clerk and Professor Hopkinson for 
copies of their papers. I am indebted also to Mr. J. T. H. 
Burrell, Assoc.M.Inst.C.E., for checking the mathematical 
calculations and for working out the examples. For the 
illustrative matter I have to thank the Institutions, Firms and 

v 



vi PREFACE TO FIRST EDITION 

individuals mentioned in the following list, but chiefly my 
friend Mr. F. Strickland and Messrs. Chas. Griffin & Co. for 
permission to reproduce certain illustrations from their " Petrol 
Motors and Motor Cars." Finally I tender my thanks to the 
Editors of The Engineer and Engineering for permission to 
reproduce certain parts of articles contributed to their columns. 

H. E. W. 

Chelsea 

IWi August 1908 






PREFACE TO SECOND EDITION 

Since the First Edition of this book was printed there have 
been many important developments in the internal combustion 
engine. There has been a considerable extension of its use 
at sea, a very largely increased employment on land, and a 
most notable development for service in the air. Moreover, the 
recent work of the B.A. Gaseous Explosions Committee has 
provided a real basis for a modern theory of the engine. These 
changes in theory and practice have necessitated corresponding 
changes in the book ; the new matter to be added has led to 
some compression in the old, so that the length might be kept 
within bounds : much has been rewritten. In this work I 
have received the valuable assistance of Mr. H. E. Piggott, 
M.A., formerly scholar of Clare College, Cambridge, and now 
Head of the Mathematical Department of the R.N. College, 
Dartmouth, and of Mr. W. E. Hogg, A.R.C.S., Assoc.M.Inst. 
C.E. ; to both of them my thanks are due. 

At the end of each chapter will be found some problems 
for solution, drawn chiefly from the examination papers set 
at Cambridge, at the Imperial College of Science and 
Technology, and by the Board of Education and other 
Government Departments. These have been arranged by 
Mr. Piggott, and his solutions of them are given at the end 
of the book. 

H. E. W. 
Hampstead 

28th February 1915 



vi 1 



The Author is indebted for Illustrations to the 

following : 

The Institution of Civil Engineers. 

The Institution of Naval Architects. 

The Institution of Engineers and Shipbuilders in Scotland. 

Dugald Clerk, Esq., F.R.S. 

Prof. W. E. Dalby, F.R.S. 

Prof. Bertram Hopkinson, F.R.S. 

H. A. Humphrey, Esq. 

Frederic Strickland, Esq. 

Prof. W. Watson, F.R.S. 

The Albion Motor Car Co., Ltd. 

Messrs. W. Beardmore and Co., Ltd. 

The Bosch Magneto Co., Ltd. 

The Campbell Gas Engine Co., Ltd. 

Messrs. Clement Talbot, Ltd. 

The Crosby Steam Gauge and Valve Co., Ltd. 

Messrs. Elliott Bros. 

Messrs. Grices' Gas Engine Co., Ltd. 

Messrs. Charles Griffin & Co., Ltd. 

Messrs. Richard Hornsby and Sons, Ltd. 

The Lanchester Motor Co., Ltd. 

Messrs. Mather and Piatt, Ltd. 

Messrs. Mirrlees, Bickerton and Day, Ltd. 

The National Gas Engine Co., Ltd. 

Messrs. Paraffin Carburettors, Ltd. 

Messrs. Richardsons, Westgarth and Co., Ltd. 

Messrs. John I. Thornycroft and Co., Ltd. 

Messrs. White and Poppe, Ltd. 

Messrs. Wolseley Cars, Ltd. 



IX 



CONTENTS 

PAGE 

Author's Preface to First Edition ..... v 

Preface to Second Edition . . . . . vii 

Chief Symbols used . . . . . . xiii 

Tables of Constants . . . . . . . . xv 

Molecular Weights of Gases . . . . . . xvi 

CHAPTER I 

Elementary ......... 1 

History of Internal Combustion Engin3 — Use of Com- 
pression — Comparative Economy. 

SECTION I — THEORY 

CHAPTER II 

Thermodynamic Cycles . . . . . . .11 

Units — Perfect Gas — Isothermal Expansion — Adiabatic 
Expansion — -Entropy — Constant Temperature Cycle — Con- 
stant Pressure Cycle — Constant Volume Cycle — Air Standard. 

CHAPTER III 

Combustion and Explosion. . . . . . .44 

Chemical Combustion — Dugald Clerk's and Grover's Early 
Experiments on Explosion in Closed Vessels — Discussion of 
Results — Increase of Specific Heats of Gases- — Dissociation 
— " After-burning " — Later Explosion Experiments — Time 
of Explosion — -Turbulence — Gaseous Explosions Committee. 

CHAPTER IV 

Thermodynamics . . . . . . . .66 

Internal Energy — Joule's Law of Thermodynamics — -Effect 
of increasing Specific Heat — Form of Adiabatic — Measure- 
ment of Cylinder Temperature — Gas Standard of Efficiency 
— Flow of Heat through Metal Walls of Cylinder — Heat 
Paths. 

xi 



xii CONTENTS 

SECTION II— GAS ENGINES AND GAS PRODUCERS 

CHAPTER V 

PAGE 

The Gas Engine 103 

Modes of Action — Types of Engine- — Humphrey Gas Pump 
- — Gas Turbine — Methods of Improving Efficiency — Indi- 
cators and Indicator Diagrams — Heat Balance Sheets- — En- 
gine Tests — Governing — Cyclic Irregularity — Balancing. 

CHAPTER VI 

The Gas Producer . . . ' . . . . 170 

Theory- — Typical Suction and Pressure Producers — Tests 
— Costs- — Use of Gas Producer for Marine Purposes — Appen- 
dix containing Description of Mode of Operation of Suction 
Gas Plant. 

CHAPTER VII 

B last-Furnace and Coke- Oven Gases . . . .205 

Thermal Value- — Cleaning the Gas — Utilization of the 
Surplus Power. 

SECTION III— OIL AND PETROL ENGINES 

CHAPTER VIII 

Oil and Petrol Engines . . . . . . .219 

Fuels — Slow-speed Oil Engines — Diesel Engine — Petrol 
Engines for Motor Cars and Aircraft— Carburettors- — Theory 
of Jet Carburettors- — Ignition. 

CHAPTER IX 

Petrol Engine Efficiency and Rating . . . .277 

Efficiency Tests under Various Conditions — Effect of 
Cylinder Dimensions on Power and Efficiency — Engine 
Rating — R.A.C. Rule — Callendar Rule— Operation of Two- 
Stroke Engine — Composition of Exhaust Gases as related to 
Efficiency- — Motor Vehicle Tests. 

Answers to 'Examples . . . . . . . 3C6 

Index .......... 309 



LIST OF CHIEF SYMBOLS USED 



P = Pressure 

V = Volume 1 

T = Temperature absolute (Centigrade) 

6 = Temperature (Centigrade) as read by thermometer 

E = Internal energy 

(p= Entropy 

v = Velocity 
C p = Specific heat at constant pressure 
Ct, = Specific heat at constant volume 

J = Mechanical equivalent of heat or " Joule's Equivalent " 
t = Time in seconds 

r] = Efficiency 
C P 

y — - 
r C, 

a) = Angular velocity 

I = Moment of Inertia 
I.H.P. = Indicated Horse-Power 
B.H.P. = Brake Horse-Power 
k\V = Kilowatts 

r = Compression-ratio 



x.n 



USEFUL CONSTANTS 



Length, Area and Volume 

1 centimetre = 0-3937 inch. 

1 inch = 2-540 cm. 

1 sq. cm. = 0-1550 sq. in. 

1 sq. in. — 6-452 sq. cm. 

1 cu. metre = 35-31 cu. ft. 

1 imperial gallon = 4-546 litres — 10 lb. of water. 

1 U.S.A. gallon = 3-785 litres. 

Weight and Pressure 

1 kg. = 2-205 lb. 

g = 32-2 ft. per sec. per sec. = 981 cm. per sec. per sec. 

1 atmosphere = 14-7 lb. per sq. in. = 760 mm. of mercury 

= 2,116 lb. per sq. ft, = 34 ft. of water. 
1 lb. per sq. in. = 0-07031 kg. per sq. cm. 
1 litre of water weighs 1 kg. = 1000 grams. 
1 metric ton = 2205 lb. 

Energy 

1 ft. lb. = 0-1383 kg. metre = 1-356 x 10 7 ergs. 

1 Joule = 10 7 ergs = 0-7373 ft, lb. 

1 H.P.-hour = 1,980,000 ft. lb. 

1 C.H.U. = 1,400 ft, lb. 

1 B.Th.U. = 778 ft. lb. 

1 calorie = 3,087 ft. lb. = 2-205 C.H.U. 

Power 

1 watt = 1 volt. X 1 ampere = 10 7 ergs, per sec. = 1 Joule 

per sec. 
1 K.W. = 1-34 H.P. = 0-239 calories per sec. 
1 H.P. = 0-746 K.W. = 76-04 kg. m. per sec. 
1 metric H.P. = 0-986 English H.P. = 75 kg. m. per sec. 

xv 



XVI 



CONTEXTS 



Other Constants 

1 cu. ft. of water = 62-3 lb. 
1 cu. ft, of air (X.T.P.) - 0-0807 lb. 
1 radian =57-3 deg. 
log,.r = 2-3026 x log 10 x. 
e = 2-7183. 

Absolute zero = -273° C. = - 459 : F. 

Approximate atomic weights: O. 16: H. 1 ; C, 12 ; N. 14.' 
Average composition of air, 23 per cent, of oxygen by weight or 
21 per cent, by volume, remainder almost entirely nitrogen. 



MOLECULAR WEIGHTS OF GASES 



Gas 



Carbon dioxide 
Carbon monoxide 
Ethylene . 
Methane 

Oxygen 
Water vapour 
Hydrogen 
Nitrogen 



Formula 


Molecular 
Weight 


co 2 


44-00 


CO 


28-00 


C0H4 


28-03 


CH 4 


16-03 


0, 


3200 


HoO 


18-02 


H., 


2-016 


N 2 


28-02 



CHAPTER I 

Elementary 

History of Internal Combustion Engine — Use of Compression — 
Comparative Economy. 

1. Heat Engines. — Heat engines are machines which receive 
heat and turn some portion of it into mechanical work. They 
are of two kinds — 

(1) Steam Engines 

(2) Internal Combustion Engines. 

In steam engines the heat is applied to the boiler which 
generates steam. The steam passes through the steam pipe 
into the engine, and when it gets there it makes the engine 
do work. 

The internal combustion engine works in a different way 
altogether. The heat is actually produced by combustion of 
fuel inside the cylinder of the engine. Whereas the steam engine 
illustrates external combustion. Gas, oil and petrol engines 
are called internal combustion engines. A gun is also a form 
of internal combustion engine in which a certain part of the 
heat given out on explosion is converted into kinetic energy in 
the projectile. 

2. History of the Internal Combustion Engine. — The first 
internal combustion engine was made by Huyghens in the 
year 1680. It was very different to any engine made now. It 
did not work on gas or oil or petrol, but used gunpowder as its 
fuel. Gunpowder was exploded in a hollow cylindrical vessel 
while the piston was at the top, and the air was driven forcibly 
out. The partial vacuum so caused, tended to pull the piston 

1 B 



2 THE INTERNAL COMBUSTION ENGINE ;chi?. : 

down, and this force could be applied by means of a cord and 
pulley to raise a weight or to do work by some other suitable 
mechanism. This engine was not a practical success, nor were 
any later engines working with gunpowder as fueL In the 
year 1820 the first engine that could really be called a " gas 
engine " was made. Its inventor was the Rev. W. CeeiL who 
by an ingenious arrangement exploded in the working cylinder 
hydrogen gas mixed with air. the principle being the same as 
that of the Huyghens gunpowder engine. This also was not a 
practical success, though a step forward. 

3. Lenoir Engine. — The first engines that could be put to 
practical use were made by Lenoir in 1860. He used the ideas 
of many people who had previously been working at the 
subject, but he grasped the matter more thoroughly and much 
more constructively. Many hundreds of his engines were made. 
His plan was to draw into the cylinder a mixed charge of air 
and gas. This he did by causing the connecting rod to pull 
the piston upwards, then when the piston was half way up the 
cylinder he ignited, by an electric spark, the gaseous mixture 
which had been drawn in. The gas could not escape by the 
inlet pipe, as that contained a non-return valve. So the full 
effect of the explosion was felt by the piston, which was forced 
upwards causing the connecting rod to do work. When the 
pis :on reached the top of its stroke the outlet valve was opened. 
Then since the connecting rod was fastened to a crank which 
turned a fly-wheeL the energy of the latter made the piston 
descend and drive the burnt products out of the cylinder. It 
then began to rise again, drawing in a fresh charge of gas and 
air. winch was in turn ignited when the piston was half way up 
the cylinder. Thus the motion was repeated. The air and gas 
"rre always drawn in at about atmospheric pressure, and were 
ignited by the spark at that pressure. In modern engines the 
mixture of gas and air is always compressed before ignition. 
Lenoir's engine is therefore called a " non-compression " engine. 
It used about seven times as much fuel per horse-power as 

4. Otto and Langen. — In 1866. Otto and Langen produced 
an engine in which the piston was not fastened to a connecting 
rod. but was loose and could fly upwards. When the 



CHAP. I] 



ELEMENTARY 



ploded gases had expanded and had got cool (partly by expan- 
sion and partly by the effect of the cold cylinder walls), the 
flying piston stopped rising and began to fall under gravity. 
It was then caught by a kind of ratchet on its connecting rod, 
and, using its weight in this way, the piston did work. This 
engine was not very successful, its action being spasmodic. 
But in 1876 Otto produced what he called a " silent engine " 
— to distinguish it from the noisy flying piston engine just 
described. It worked on a principle of operation which had 
been very clearly stated fourteen years before by Beau de 
Rochas, who, although he had patented it, had not made a 
working success of the invention. Otto was a more practical 
man, and he made his new engine very successful. The 
method of working was as follows : — 

( 1 ) Air and gas were drawn in during an outward stroke of 

the piston, followed by 

(2) Compression of the mixture during the return inward 

stroke. 

(3) Ignition at the inner dead centre, and expansion through- 

out the next outward stroke. 



Inlei- 1/a.he 



Connectmq 
Rod 




Outer 
Dead Centre 



Combustion 
Chamber 

Exhaust Valve 

Fly Wheel 

Fig. 1. — Diagram of Otto Engine. 

(4) Discharge of the burnt gases on the return of the piston 
during the last stroke. 

This cycle of operations takes, it will be noticed, four strokes 
to complete, and is known as an " Otto-cycle " or " Four- 
stroke " cycle. 

5. Use of Compression. — The fundamental difference between 
the Lenoir and the Otto engines lies in the fact that the former 
was a non-compression engine, whilst the latter employed 



4 THE INTERNAL COMBUSTION ENGINE [chap, i 

compression. A further difference is that the Lenoir engine 
completed its cycle of operations in two strokes, and is known 
as a " two-stroke " engine, whilst the Otto engine is a " four- 
stroke " one. The advantage of compression is that the gases 
are at a fairly high pressure before the ignition point is reached, 
and so the effect of the explosion is to cause the mixture to 
reach a far higher pressure, and therefore to do more work, than 
if the pressure before explosion were no higher than that of the 
atmosphere outside the engine. The fact that all engines work 
on compression means that all must have a space provided into 
which the piston can compress the charge. This space is called 
the " clearance space." In Fig. 2 the face of the piston, at the 
end of compression, comes up to the line AB, and on the expan- 
sion stroke moves out as far as EF. Then the space between 
AB and CD is called the "' clearance " ; the distance from AB 
to EF the " stroke " ; and the ratio of the volumes CDFE to 
CDBA the " compression ratio," denoted by the letter r. It 
is obvious that the higher the compression ratio the higher will 
be the pressure at the end of compression, and thus the higher 
will be the temperature at that point. 




Fig. 2. — Diagram of Cylinder and Piston, showing clearance. 

. * x . volume C E F D 

Compression ratio = — . — — -= — .-,_. . 
^ volume C A B D 



6. Dugald Clerk. — In 1880 Dugald Clerk invented an 
engine which partook of the nature of the Lenoir in that it 
was a two-stroke engine, and of the nature of the Otto in that 
the mixture was compressed before explosion. This he did by 
mixing and slightly compressing the gas and air in a separate 
cylinder instead of in the working cylinder. The working 



chap, i] ELEMENTARY 5 

cylinder received its mixture of gas and air under slight com- 
pression, forcing out the exhaust gas as it entered, so that the 
exhaust and drawing in strokes could be omitted in the main 
cylinder. Of course the operations thus omitted in the main 
cylinder had to be done in the other cylinder — called the pump 
cylinder — but the working cylinder was able to effect twice 
as many working strokes per minute as before. The work 
done by this cylinder was therefore doubled, but against this 
must be set the work lost in pumping in the other cylinder. 
Engines working on the Clerk cycle are now made in consider- 
able numbers. 

7. Daimler . — In 1895 Daimler brought out his well-known 
high speed petrol engine for automobiles. The Otto cycle 
was followed, and the chief improvements were of a mechanical 
nature. Petrol vapour was used instead of gas. This engine 
gave a great impetus to mechanical transport on roads and 
to the use of motor-boats. 

8. Diesel. — In 1897 a novel form of oil engine was intro- 
duced by Diesel. Instead of a combustible mixture of oil- 
vapour and air being drawn in on the suction stroke, air only 
was allowed to enter. This was compressed to a very high 
pressure on the compression stroke — 500 lb. per sq. inch — 
and was raised by this compression to a high temperature. 
Then at the inner dead centre a small quantity of oil was 
injected at an even higher pressure (800 1b. per square inch) 
by means of compressed air. This oil at once ignited on 
coming into contact with the air, and forced the piston on its 
outward stroke. As the stroke continued, more oil was 
injected until the " cut-off " point was reached, when the 
gases were allowed to expand and do work in the usual way. 
The effect of admitting the fuel gradually, instead of all at 
once, was to get a more even pressure on the piston from the 
beginning of the stroke until the cut-off point. This made 
the action of the engine similar in some respects to the action 
of the steam engine, where the principle of gradual admission 
also applies. In this engine no electric spark was needed to 
ignite the mixture, since the temperature of the air at the end 
of compression was itself high enough to cause combustion to 
take place. 



6 THE INTERNAL COMBUSTION ENGINE [chap, i 



9. Humphrey Gas Pump. — A new type of engine was 
introduced by Humphrey in 1909, in which the iron piston 
was replaced by the flat surface of a vertical water column 
which under the explosive force of the gaseous mixture was 
made to oscillate in a series of unequal strokes, and in so doing 
to cause water to pass from a low level tank to a high level 
one. The water so pumped could if desired be made to work 
a water turbine. 



Useful 
i work. 



Loss in 

Engine 

friction 



L_0S$ in 
Engine 
Coolinq 
Water. 



Loss By 
Radiation 
dtcfrom 
•Producer. 




Loss In 
Engine 
Exhaust 



Energy in Cos /. 
Fig. 3. — Efficiency Diagram of Gas Power Plant. 



10. Comparative Economy of Steam, Gas and Oil. — An 

interesting comparison of the relative fuel consumptions 
and capital costs was made by T. E. Wollaston, in a paper 
read before the Society of Chemical Industry in 1914. The 
following is an extract from his paper : — 

For purposes of comparison the following is an approxi- 



CHAP, i] 



ELEMENTARY 



mate table showing the performance and cost of modern 
prime movers. The various units are : — 

(a) The most economical form of modern steam engine 
in conjunction with modern boiler plant. 

(b) A steam turbine of highest class with modern boiler 
plant. 

(c) Gas engine with " bituminous " gas plant. 

(d) Diesel oil engine. 



Type 


B.Th.TJ. 
per B.H.P. 

hour 


Fuel cost 
per B.H.P. 

hour 


Capital 

cost per 

B.H.P. 


{a) Steam engine . 
(6) Steam turbine . 

(c) Gas engine .... 

(d) Diesel engine 


19,000 

21,000 

15,000 

9,000 


0-102d. 
0-112d. 
0-08d. 
0-18cZ. 


£7 
£6 
£8 
£8 



In the above 70 per cent, efficiency is assumed for boiler 
and gas plant. Coal of 10,000 B.Th.U. per lb. at 12s. per ton. 
Diesel oil of 18,000 B.Th.U. per lb. at 70s. per ton. 

In Fig. 3 is seen a diagrammatic representation of the way 
in which the fuel energy is used in a gas engine and producer 
plant. 



SECTION I 



THEORY 



CHAPTER II 

Thermodynamic Cycles 

Units — Perfect Gas — Isothermal, Expansion — Adiabatic Ex- 
pansion — Entropy — Constant Temperature Cycle — Con- 
stant Pressure Cycle — Constant Volume Cycle — Air 
Standard. 

11. Quantity of Heat. — The quantity of heat given to the 
water in a vessel is measured by multiplying the weight of the 
water in pounds by the rise in temperature of the water due to 
its receiving this heat. Thus if 40 lb. weight of water be 
heated so that its temperature rise from 50° C to 75° C the 
quantity of heat supplied is 40 X 25 — 1,000 heat units, and 
as the temperature scale used is Centigrade these heat units 
are called Centigrade heat units (C.H.U.) or pound-calories. 
The equality of 1,000 pound-calories to 1,800 B.Th.U. can be 
immediately seen, as one degree Centigrade is equal to 1*8 
degrees Fahrenheit. One pound-calorie is the amount of 
heat required to heat one pound weight of water through one 
degree Centigrade. One B.Th.U. is the amount of heat 
required to heat one pound weight of water through one degree 
Fahrenheit. When the unit of weight is the kilogram and the 
Centigrade scale of temperature is used, the unit of heat is 
called the Kilogram-calorie. 

12. Specific Heat. — The above definitions have all been 
expressed in the terms of heating water ; water being the most 
convenient standard substance to select, and having, as it 
happens, a greater capacity for heat than any other known 
liquid. Thus one pound-calorie will heat one pound of water 
through one degree Centigrade, but it would heat one pound 
of mercury through no less than 30 degrees Centigrade. The 
specific heat of a substance is defined as the quantity of heat 

11 



12 THE INTERNAL COMBUSTION ENGINE [chap, n 



necessary to raise one pound weight of that substance through 
one degree of temperature. The following are the specific 
heats of some of the commoner substances : — 



Water .... 






1-000 


Mercury .... 






0033 


Brass .... 






0-090 


Cast Iron .... 






012 


Lead ..... 






0-030 


Glass . . . . 






0-19 


Air 






0-24 



Thus 0-030 pound-calorie are needed to heat one pound of lead 
through one degree Centigrade, or 0-030 B.Th.L T . to heat it 
through one degree Fahrenheit. 

13. Specific Heats Of Gases. — In the study of the behaviour 
of a perfect gas it is usual to assume that the specific heat 
is independent of the pressure and tempera tine. In real 
gases this is found to be only approximately correct, since the 
specific heat, though practically independent of the pressure, 
does increase substantially with increase of temperature. This 
is illustrated in Fig. 21 on p. 63, where the specific heat of the 
expanding gases in a gas engine is shown plotted against the 
temperature. When measurement is being made of the 
specific heat of a gas, it is possible to keep either its volume 
or its pressure constant. The former specific heat is called 
the specific heat at constant volume, and is usually denoted 
by C v , the latter is the specific heat at constant pressure and 
is denoted by C r The specific heats at constant pressure 
will always be larger than those at constant volume, because 
the gas, in expanding, expands against the atmospheric pressure 
and therefore does work. 

The following table gives the constant-pressure specific heat 



figures at C 



C 



for some of the commoner gases 



Air . 
Hydrogen . 
Carbon- monoxide 
Carbon-dioxide . 



024 
3-40 
0-24 
0-20 



In gas engine work the simplest plan is to take a mean value 
for the specific heat over the temperature range considered. 



chap. II] THERMODYNAMIC CYCLES 13 

14. Unit of Work. — As the purpose of internal combustion 
engines is to turn heat into work it is as important to measure 
the work done as it is the heat supplied. Work is measured 
in foot-pounds, one foot-pound being the work done in lifting 
one pound weight through a vertical height of one foot. If the 
point of application of a force of P pounds moves through a 
distance of h feet in the direction of action of the force, the 
work done is P X h ft.-lb. 

15. Volumetric Heat. — Hitherto specific heat has been 
defined as the number of thermal units required to raise one 
pound weight of the substance through one degree of tempera- 
ture ; it is sometimes convenient in the case of gases to know 
the number of foot pounds necessary to raise through 1° C. 
a mass of gas which at 0° C. and at normal atmospheric pres- 
sure (760 mm. of mercury) would occupy a volume of exactly 
one cubic foot.* This number is called the " volumetric heat " 
of the gas to distinguish it from the other way of reckoning. 
Thus it comes to exactly the same thing whether nitrogen 
is said to have a "specific heat" of 0-250 or a "volumetric 
heat " of 27-2 ft.-lb. per cubic foot. To convert specific heat 
into volumetric heat it is necessary to multiply by the weight 
in pounds of one cubic foot of the gas (at normal temperature 
and pressure) and by Joule's equivalent. f It has been found by 
experiment that for most gases the product of specific heat 
and density is a constant. The effect of this is that however 
much the specific heat figures may differ, the figures for 
" volumetric heat " are almost the same for all gases. This 
is a great convenience, as it shows that the amount of heat 
necessary to heat a cylinder full of gases, at a moderate tempera- 
ture, through any small temperature range, will be about the 
same whatever the composition of the gases may be. This 
consideration is of assistance when studying the effect of the 
presence in an explosive charge of a residuum of burnt gases 
from the last explosion, particularly when the exact pro- 
portion of the different substances in the exhaust products 
is unknown. 

* The letters N.T.P. are often added to show that the volume is 
measured at Normal Temperature and Pressure. 
t See p. 14. 



14 THE INTERNAL COMBUSTION ENGINE [chap, ii 

16. Efficiency. — The ratio of the energy got out from a 
machine to the energy put into it is called the efficiency of the 
machine. Thus 

„„, . energy given out 

Emciencv = — Cv — ~ 

energy supplied 

A gas engine usually gives out at the crank-shaft about four- 
fifths of the energy given to the piston ; its efficiency is there- 
fore said to be 0-80 or 80 per cent. This is called the median ical 
efficiency, to distinguish it from the thermal efficiency, which 
is the ratio of the energy given to the piston to the energy 
contained in the fuel used, and rarely exceeds 30 per cent, in 
any engine. 

17. Unit of Power. — When a machine is capable of doing 
33,000 ft. -lb. of work every minute (or 550 ft. -lb. every second 1 . 
it is said to be of one horse-power, or 1 H.P. 

As the work done in a minute by 1 H.P. is 33,000 ft. -lb., 
so the work done in an hour is 60 / 33,000 ft. -lb., or 1,980,000 
ft. -lb., which is therefore the equivalent of 1 H.P. -hour. Ano- 
ther unit of power, derived from electrical practice, is the 
kilowatt ( or kW. | It is larger than the horse-power and 

1 H.P. = 0-746 kW. 

18. Mechanical Equivalent of Heat. — It was at one time 

thought that when a heat engine did work it did it by passing 
the heat without loss through the given temperature range, 
just as the work done by a waterfall depends upon passing a 
certain amount of water through a certain range of " head."' 
It is now well known that the quantity of heat supplied to an 
engine is greater than that which comes away from it. and that 
the missing part is the amount of heat that has been converted 
into mechanical work. Joule was the first to realize that heat 
could be converted into work and to measure the number of 
foot-pounds into which one heat unit could be converted. 
This he did by churning water with paddles so as to produce 
internal friction in the water. He measured the work done 
and the rise in temperature of the water : by this means the 
mechanical equivalent of 1 B.Th.U. was determined. Many 



chap, ii J THERMODYNAMIC CYCLES 15 

later and more accurate experiments have been made, and the 
result generally accepted now is that 

1 B.Th.U. = 778 ft.-lb. 
and 1 pound-calorie = 1,400 ft.-lb. 

19. Changes of State in a Gas or Vapour. — The state of a 
gas or vapour may be altered by giving heat to it, or by taking 
heat from it. The state may also be altered by compression 
or expansion. Any of these processes will bring about changes 
in one or more of such properties as — volume, pressure, tem- 
perature, internal energy, specific heat. These properties are 
related to one another in various ways, and the two most 
important of the relationships are called Boyle's Law and 
Charles' Law. 

20. Boyle's Law. — Boyle's Law states that if the tempera- 
ture be kept constant the volume of a mass of gas will vary 
inversely as the pressure. 

In symbols — 

PV == Constant 

(for constant temperature). 

21. Charles' Law. — Charles' Law states that if the pressure 
be kept constant, equal volumes of different gases increase 
equally for the same increase in the temperature ; also, that if 
a gas be heated under constant pressure equal increments in 
its volume correspond very closely to equal intervals of tem- 
perature. 

22. Absolute Temperature. — It is found by experiment that 
the amount by which the volume of gas expands when its 
temperature is changed by one degree Centigrade (the pressure 
being constant) is ^y^rd part of its volume at 0° C. If this 
proportion held rigorously for all temperatures, however low, 
it would follow that at a temperature of 273 degrees below 
0°C. the volume of the gas would be zero. The temperature 
of — 273° C. is therefore called the Absolute Zero, and tem- 
peratures reckoned from this zero instead of 0° C. are called 
absolute temperatures. Thus the boiling point of water is called 
either 100° C. or 373° C. (absolute). When using the Fahren- 
heit scale the number 459 should be added to the ordinary 
Fahrenheit temperatures to bring them to Fahrenheit tern- 



16 THE INTERNAL COMBUSTION ENGINE [chap, ii 

peratures (absolute). Charles' Law may therefore he ex- 
pressed — 

If V= volume at : C, 

and V = volume at 0°C. 

V=V— J \ls 
27 3 

= — {6+2K 
273 

= ° - T. where T = absolute temperature. 

V 
i.e.. — = constant (tor constant pressure). 

23. Perfect Gas. — A perfect gas is defined as one which 
satisfies rigorously both these laws, which may be combined 

PV 

into = constant. This constant is usuallv written B : 

T 

thus PV = RT. Most of the ordinary gases comply very 
closely with the perfect gas laws, particularly at the tempera- 
tures met with in internal combustion engines. The equation 

PV 

— = constant applies to any weight of gas ; when a standard 

weight of gas (e.g. 1 lb.) is considered, then the value of R 
depends on the nature of the gas. Tor 1 lb. weight of air 
R = 96. the units being pounds, feet and degrees Centigrade. 

24. To prove when unit weight of gas is considered that 

PV=ET=J.C P — C r )T 

where R is a constant and J is the value of the mechanical 
equivalent of heat ("Joule's Equivalent"). 

Consider one pound weight of gas (at P . V . TJ confined in 
a cylinder of exactly one square foot in cross-sectional area 
and having above it a piston whose weight may be neglect 
Let the temperature increase to T, and the volume to V ; . 
keeping the pressure constant and equal to P . 

The heat supplied to the gas = 

C T, — TJ heat units 
equivalent to JC T — T ft. -lb, 






chap, ii] THERMODYNAMIC CYCLES 17 

The external work done by the gas=P (V 1 — V ) ft. -lb. 

which=:R(T 1 — T ) ft.-lb. 
(using the equation PV=RT) 

Then the internal energy remaining in the gas must be equal 
to the difference of those two, or 

= (JC p -R)(T 1 -T ) ft.-lb. 
Now Joule discovered experimentally that the gain in internal 
energy of a gas depends only on the initial and final tempera- 
tures, and is independent of changes of pressure or volume, 
i.e., that the above increase in internal energy is the same as 
if the temperature had risen while the volume remained con- 
stant, in which case the heat units required would have been 
C^Tx— T ), or in energy units JC.CT,— T ) ft.-lb. 

Thus (JCV-RX^-To^JC^-To) 

or U=J(G p —C v ) 

This shows that the perfect gas law may be written 

PV 

^=J(C p -CJ 

a form which is often convenient. It shows also that for any 
gas which obeys the perfect gas law the specific heat at con- 
stant pressure is always larger than the specific heat at constant 
volume by the same amount, no matter what the temperature 
or pressure may be. So that if one specific heat be known the 
other, or the ratio of the two, can easily be calculated. 
25. The equation 

PV 

is true for all perfect gases, the quantity present being unit 
weight. It may be written 

|= ^ «V-c„). 

If we take two different gases, both obeying the perfect gas 
law, and adjust their pressures so as to be equal, and also their 

temperatures to be equal, the two values of — (C p — C v ) must 

be the same. But the weights of the gases being the same, 

c 





18 THE INTERNAL COMBUSTION ENGINE [chap, ii 

the volumes occupied must be inversely proportional to their 
densities. Thus (C p — C v ) X density must be a constant quan- 
tity for such gases. 

The following table shows how real gases approximate to 
this — 



Gas 


Lp 


Cv 


Density rela- 
tive to Air 


{Cp— Cv) x 
density 


H 2 . . . 


3-409 


2-406 


00692 


0069 


N 2 . . . 


0-244 


0173 


0-970 


0-069 


o 2 . . . 


0-218 


0155 


1105 


0070 


C0 9 . . . 


0-217 


0171 


1-520 


0-070 



The explanation why there are any differences at all is because 
these gases are not ''perfect gases." The assumption is im- 
plied, moreover, that the specific heat is independent of tem- 
perature, and although for many calculations this is sufficiently 
nearly true, there are others, as will appear in a subsequent 
chapter, in which this is by no means the case. 

26. Ratio of Specific Heats. — The ratio of the two specific 
heats of a gas is an important one, and is generally called by 
the Greek letter y, thus 

C 

'— r> 

7= 



Since J((L— C r )=R 



y 



i 



a 



a "j.c. 



y is usually from 1*3 to 1-4 ; and for air is exactly 1-41. 

27. Isothermal Expansion. — When a gas expands so that 
the temperature is always constant the expansion is said to be 
Isothermal. 

In symbols — 

PV= constant. 

This is, of course, Boyle's Law. 

(This is occasionally referred to asa" hyperbolic " expansion 
as the graph of the above equation is a hyperbola.) 

28. Adiabatic Expansion. — When a gas expands in such a 
way that heat, as such, is neither given to it nor taken from it, 



CHAP. II ] 



THERMODYNAMIC CYCLES 



10 



the expansion is said to be adiabatic. Such an expansion, or 
compression, may be imagined as taking place in a cylinder 
made of a completely non-conducting material, no heat being 
generated by chemical action nor lost by radiation. The more 
quickly an expansion or compression takes place, the more 
nearly is the adiabatic law followed, since there is a shorter 
time for any transfer of heat to take place. The rapid heating 
of a tyre-pump when used vigorously is a familiar phenomenon. 

is 



10 



6 



£ 



■-© 
i 

it 



---© N « 



■ — -O 



r I 2 3 4 5 £ 7 

l/glume in Cubic Feet. 

Fig. 4. — P V diagram showing compression of six cubic feet of air into one 
cubic foot, (a) Isothermal ; (b) Adiabatic. [Final pressure is more 
than twice as high in (b) as in (a).] 



When the expansion is adiabatic the law connecting P and V 
for a perfect gas can be shown to be 

PV 7 =constant. 

In Fig. 4 is shown the result of compressing a mass of gas 
from 6 cu. ft. to 1 cu. ft. Such compressions are approxi- 
mately adiabatic — see curve b — when the process is carried 
out very rapidly ; and approach the isothermal — see curve a 
— when the compression is so slow that most of the heat is 
dissipated during the time taken by the compression. 

29. Proof. — " Joule's Law," quoted in paragraph 24, comes 
to this, that the gain in internal energy due to rise of tempera- 



20 THE INTERNAL COMBUSTION ENGINE [chap, ii 

ture must equal the difference of energy due to heat supplied 
and the work done. 

Thus, if AH heat units are supplied to unit weight of gas 
J.C r . AT= J. AH— P. AV 
where AT and AV are increments in temperature and volume. 

If the gas is neither to receive nor to lose heat 

AH=0 

and the equation simplifies to 

J.C v AT+P.AV=0. 

Now in any finite transformation P will be continually chang- 
ing, and the process must therefore be imagined to be split up 
into a great number of infinitesimal steps. Consider AT and 
AV as infinitesimal increments, and obtain the equation con- 
necting P and V by integration, thus : — 

J.C„.AT+P.AV=0 

from pars. 24 and 26, PV=J.C„.(y— 1)T 
therefore P. AV+V. AP=J.C v (y— 1) AT 

=— (r— i)P.av 

therefore V.AP= — y .P. AV 

^+y^=0 
P T/ V 

in the limiting case -f- y =0, 

& p rr y 

therefore log P+y log V=constant, or PV 7 = constant. 
30. Temperature Changes in Adiabatic Transformations. — 

The adiabatic law for a perfect gas is 

PV Y = constant ; 
combine this with the perfect gas equation of 

PV=RT 

and eliminate P 

then TV^ 1 ^ constant ; 

or V can be eliminated and then 

rjiy 

— -= constant. 

py 1 

If, therefore, the initial state of a mass of gas be known it 



cha*. n] THERMODYNAMIC CYCLES 21 

is possible to calculate its temperature at any point after adia- 
batic expansion or compression from a knowledge either of its 
new volume or of its new pressure. 

Both the laws discussed in paragraphs 27 and 28 are special 
cases of the general formula PV n = constant, n being equal 
to unity in the isothermal case and equal to y in the adiabatic 
case. In the internal combustion engine the gas does not 
expand or compress according to either of these laws precisely, 
but the expansions and compressions do in every case follow 
very nearly some law of the type PV W = constant, where n 
has a value lying between unity and y. 

Example.- — If the gas during a compression stroke increased 
in pressure from atmospheric pressure to 65 lb. per sq. inch 
above the atmosphere, and if the temperature before compres- 
sion were 120° C, the temperature at the end of compression 
could be calculated from the equation in par. 30. 



>n-l 



= constant 



and if n be 1-3 
Then 



T 1 ' 3 (120 +273) 1 ' 3 



t0-3 /-\A.n\0-3 



(14-7 +65) u '° (14-7) ( 

/7O.7\0j* /79-7\ ' 23 

or T=(120+273H— V-3 = 393(_j 

or T = 580° C. (absolute) = 307° C. 

This explains how it is that a gas gets hot when compressed 
so suddenly that there is little time for heat to escape through 
the w r alls of the cylinder. 

31. The Thermodynamic Laws. — The following are the two 
fundamental laws of thermodynamics. 

(1) In all transformations, the energy due to the heat units 
supplied must be balanced by the external work done plus the 
gain in internal energy due to the rise in temperature. 

(2) It is impossible for an automatic machine, unaided by any 
external power, to convey heat from a colder to a hotter body. 

The first of these laws was discovered experimentally by 
Joule. It has been stated in paragraph 29, and was there 
interpreted in symbols, viz. : 

J.AH=JC,AT+PAV 



22 THE INTERNAL COMBUSTION ENGINE [chap, ii 

The second law may be said to represent universal experience 
in the working of heat engines. 

32. Thermal Efficiency.— So far as the first law is concerned 
there is nothing to show why all the heat supplied to an engine 
should not be converted into work. But the effect of the 
second law is that only a portion of the heat supplied can be 
converted into work, and, as stated in par. 16, the ratio 

Heat converted into work 
Heat supplied to engine 

is known as the thermal efficiency of the engine. The better 
the engine the higher the efficiency. The most efficient heat 
engine yet built has an efficiency of about 0-4. 




V Volume ]/, 

Fig. 5. — PV diagram. 

33. Application of Graphical Methods to Thermo-dynamics ; 
Pressure-Volume and Temperature-Entropy Diagrams. — The 

reader is probably familiar with graphical methods as applied 
to physical problems. In many such cases it is customary to 
deal with three physical quantities ; two of these are plotted 
along the axes of co-ordinates, and the relation between them 
exhibited by the graph, while the third is involved in the area 
contained between the curve and one of the axes. 

If pressure (lb. per sq. ft.) be plotted along one axis and 
volume (cu. ft.) along the other, as shown in Fig. 5, the area 
between the curve and the X axis, bounded bv the ordinates 



CHAP. Il] 



THERMODYNAMIC CYCLES 



23 



at V = V and V = V l3 will give the external work done (ft.- 
lb.) when the volume of the gas increases from V to V^ 

Proof.— Area of shaded strip = P. AV, which is work done 
by pressure in increasing volume by AV. Therefore total 
work done = 2P. AV for all such strips (or in calculus nota- 
tion, I P.tfV) which is the area under the curve. 

It is this principle that enables the work done by an engine 
to be calculated from an indicator diagram showing the pres- 
sures and volumes of the working medium. 

In some problems, however, it is convenient to have the 
temperature shown along the Y axis, and the area under the 




fy Entropy <^ 

Fig. 6. — T0 diagram. 

curve to show, not work done, but heat units supplied to the 
gas. The question arises, what, in this case, is to be plotted 
along the X axis ? The answer to this question is that the 
quantity to be plotted along the X axis is not one like pressure 
and volume with which acquaintance has already been made, 
but a new one, and one which cannot be measured directly. 
The name given to it is entropy. It is not possible to give a 
simple scientific definition of entropy, nor is it necessary to do 
so. It is obviously some property of the state of a gas which 
determines the connexion between rise of temperature and 
increase of heat units. If we keep in mind the graphical in- 



24 THE INTERNAL COMBUSTION ENGINE [chap, ii 

terpretation as explained above, it is unnecessary to express 
the idea of entropy in any formal definition.* In Fig. 6 such 
a graph is given. The area under the curve, and lying between 
the ordinates at (p and q? l3 measures the number of heat units 
supplied to the gas between the temperatures T and T i. 

Calculation. — Calling the entropy cp, the area of the shaded 
strip = T. A cp, but this by definition is equal to AH, 

therefore T. A cp = AH 

AH 

or A 9? = 



and op = I 



T 
clH 



T 

From this formula the actual value of the entropy in a mass of 
gas can be calculated. 

34. Unit of Entropy. — If the area under the curve in Fig. 6 
were 1000 pound-calories and the temperature had remained 
constant at 500° C. (absolute), corresponding to an isothermal 
expansion, the curve would have been flat, i.e. a straight line 
parallel to the axis of entropy, and it is clear that the difference 
(<Pi — <Pz) would have had to be two units of entropy in length, 
so that 

2 x 500 = 1000 pound-calories. 

One unit of entropy would therefore be the amount of increase 
in entropy due to the reception of a number of heat units equal 
in amount to the absolute temperature at which the heat is 
received, and this unit of entropy is called 1 rank. 

The temperature values used in entropy calculations must 
always be absolute. The importance of temperature-entropy 
graphs lies chiefly in their applications to isothermal and 
adiabatic transformations : — 

(1) In isothermal transformations the temperature is con- 

stant, so that the graph will be a straight line parallel 
to the entropy axis. 

(2) In adiabatic transformations no heat units are gained or 

lost, so that the entropy remains constant and the graph 
will be a straight fine parallel to the temperature axis. 

* Readers desiring to get a fuller idea of entropy are referred to 
Professor Callendar's address to the Physical Society, of which an 
abstract is given on p. 97 of Nature for March 16, 1911. 



chap, ii] THERMODYNAMIC CYCLES 



25 



This means that any closed circuit made up of successive iso- 
thermal and adiabatic compressions and expansions will have 
a graph composed exclusively of straight lines at right angles 
to one another. Hence the area can be very easily measured, 
and the amount of heat supplied be readily determined. 

35. PV and T^ Diagrams Compared. — The following state- 
ments help in memorizing the relationships between these two: — 

(1) Average force (lb.) X space range (ft.) = work done (//.- 

lb.), or, what comes to the same thing, average pressure 
(lb. per sq. ft.) X volume range (cu. ft.) = work done 

(ft.-a.). 

(2) Average temperature (absolute) X entropy range (ranks)= 

heat units, — the latter being either calories or B.Th .U. 



25 



2C 



10 



>-V 






Pa 



VOLUME 




Fig. 7.- 



6- 
i <- 

_J Entropy (ranks) 

PV and T<p diagrams for Constant-volume Cycle. 



according as the temperature (absolute) has been measured in 
the Centigrade or Fahrenheit scales. 

36. Areas Of Closed Cycles.— After any ideal cycle of opera- 
tions, when the gas returns to its initial state, both the PV and 
T cp diagrams will be closed figures ; in this case the net work 
done (in the PV diagram) and the net heat units taken (in 
the T cp diagram) will be given by the area of these closed 
figures. 

Thus the PV and T cp curves shown in Fig. 7 are those of the 




THE INTERNAL COMBUSTION ENGINE [chap, h 

"" Otto " cycle on which most modern gas engines work, and 
they will be referred to at greater length in this book. 

The area under the curve T_T : = heat units received. 

The area under the curve T S T = heat units rejected. 

Thus the area contained within the closed figure TeT^T^Tj 
gives the number of heat units which are converted into work 
by the engine. If this be multiplied by the numerical value 
of J. it will give the same result as would be obtained by measur- 
ing the area of the figure PoPiP.P 




F 



Fig. 8. 



The PV and T rp diagrams therefore have this in common, 
that the area of the closed figures in each, corresponding to 
a given cycle of operations, will give the work done. The 
thermal efficiency can be obtained very simply from the T . 
diagram since 

area T(,TiT 2 T 3 



Thermal efficiencv = 



area under T T 



In Fig. 8 is shown a very simple entropy diagram for one 
pound of gas. The gas starts at the point A : the temperature 
is then increased to the point B. whilst the entropy remains 



(hap. n] THERMODYNAMIC CYCLES 27 

constant — an adiabatic compression; then the gas has its 
temperature kept constant from B to C, whilst the gas receives 
heat and the entropy increases — an isothermal expansion ; then 
from C to D the gas expands adiabatically as the entropy is 
constant and the temperature falls to D ; then from D to A 
the temperature remains steady, whilst the gas gives up its 
heat and the entropy diminishes from D to A, so bringing the 
gas back to its original state, and ready to go through the 
cycle again. This is the well-known Carnot Cycle, which is 
so often shown on the PV diagram, but is so much more 
easily understood on the T 99 diagram. 

T ,, . x1 , ™ ■ area ABCD AB 

In this case thermal efficiency = — = 

J area EBCF EB 

_ max. temp, of cycle — min. temp, of do. 
max. temperature of cycle 

which is the customary expression for the efficiency of the 
Carnot Cycle. This is an instance of how simple the use 
of the T cp diagram makes such calculations. 

37. In this last named figure all the lines were parallel to 
one or other of the axes. This was because an ideal cycle 
of the simplest nature was being followed. In Fig. 9 the 
sloping lines AB and BC have been drawn at random. What 
changes of state would they represent ? 

The line AB shows an increase of both entropy and tem- 
perature, both of them increasing at about an equal rate. 
So that heat is being given to the gas, and the temperature 
is increasing meanwhile. This is generally similar to what 
goes on during explosion in a gas engine cylinder, as the gas 
takes in heat from the effect of chemical combination, and 
the temperature rises while it does so. Having arrived at 
the point B the gas now follows the line BC, during which 
the gas continues to take in heat, and the temperature decreases. 
This is what would occur, on a lesser scale, in a gas engine 
cylinder were the combustion of the gas to continue right 
through the working stroke instead of ending at the point 
of highest temperature, as it is now generally believed to do. 
Then to get the gas back to its original state the line CA is 
followed, and during it the gas gives out its heat at a nearly 



28 THE INTERNAL COMBUSTION ENGINE [chap, rl 



steady temperature, i.e. almost an isothermal compression. 
No gas engine works exactly on this cycle, which was one 
drawn at random to show how any cycle whatsoever can be 
very easily and readily studied by the use of the T cp diagram. 
It is obvious from the diagram that the efficiency of this 
triangular cycle would be a low one as the area is small having 
regard to the temperature variation represented. 




Fig. 9. 



Gas engine indicator diagrams are often turned into T 99 
diagrams, but it is necessary that certain precautions should 
be taken in doing so. The difficulty lies in the fact that the 
working fluid does not remain in the cylinder for a number of 
cycles, but is periodically discharged to exhaust, and a fresh 
charge brought in. The cycle can, however, be treated as a 
continuous one if the exhaust gases are considered to have 
their relatively high temperature and pressure reduced to 
those of the incoming charge, the volume being kept constant. 
In an Appendix to an Institution of Civil Engineers report * 
Captain Sankey has shown a number of PV and T 99 diagrams 
for the same gas engine cycles, and by the permission of 

* I. C. E. Proc, Vol. 162. 



CHAP. Il] 



THERMODYNAMIC CYCLES 



29 



the Council of the Institution, one of them is reproduced in 
Fig. 1 0. The outer lines show the T <p and PV diagrams for 




Fig. 10. 



an ideal engine, whilst in the shaded portion is given the 
same diagrams for a probable actual engine. The wavy part 
of the entropy curve shows the expansion period of the cycle. 



30 THE INTERNAL COMBUSTION ENGINE [chap, n 

It has been drawn to show the loss of heat to the walls and 
piston during the beginning of expansion, and the subsequent 
flow of heat in the reverse direction during the latter part of 
the stroke.* this effect dying away again at the very end of 
the stroke, possibly on account of the slow motion of the 
piston at that point, which would allow the walls a greater 
amount of time in which to part with their heat. 

Before dealing with the efficiencies of the various cycles 
of working it is necessary to say something about the work- 
ing medium. The gaseous mixture that enters a gas engine 
(for oil or petrol engines the same considerations apply) is 
usually y 9 ^ air and the rest gas. and even when the proportion 
of air is not quite so high as this, by far the greater part of the 
mixture is simply air. Air is in fact the working substance. 
and gases, oils and petrols are used merely to raise its tempera- 
ture to the point required to carry out the predeterniined 
cycle of operations. So that although the thermal constants 
are given not only for air but also for other gases, etc .. it must 
be remembered that air is the most important factor, and that 
inasmuch as air is i nitrogen, it is the latter gas which is most 
concerned, however passively, in the working of internal 
combustion engines. The following table shows the composi- 
tion of the fuel gases chiefly in use, and their approximate 
calorific values. 



TcrCTTi !- - 


Producer Gas 


Blast Furnace 
Gas 


Coke- Oven 
Gas 


CO .... 


per cent. 
7 


per cent. 
20 


per cent. 
25 


per cent. 
8 


CO, .... 


2 


9 


6 


2 


H .... 


46 


21 


_ 


\ 


X .... 


3 


48 


66 


5 


Hydrocarbons 


42 


2 


1 


32 


B.Th.U. per cub. 










ft. about 


600 


150 


90 


U 



38. Ideal Standard Cycles. — Every one who is acquainted 

* Tt would have been more accurate to have shown a continuous 
loss of heat by the ga> — - ■; \ ar. 59. 



chap, ii] THERMODYNAMIC CYCLES 31 

with steam engines knows that the standards of comparison 
are the Carnot Cycle and the Rankine Cycle, that is to say, 
these two ideal cycles of operation are the standards by which 
actual engines are best judged. It would be unfair to com- 
plain of any engine which gave a thermal efficiency of 
0-27 when that ideally possible for the temperatures employed 
was only 0-30, indeed such an engine must be greatly superior 
to any yet constructed, and although 27 per cent, efficiency 
does, it is true, mean that 73 per cent, of the energy is wasted, 

•27 
yet in reality the engine is a very good one as it yields — , 

* oU 

i.e. 90 per cent, of what is ideally possible. It is this figure of 
90 per cent, which should really be looked to. The figure 
of 0-27 gives little information, but the figure of 90 per 
cent, shows at once that unless the manner of working be 
altogether changed there is only 10 per cent, left to improve 
upon. In a steam engine the endeavour is to keep the cylinder 
hot and so prevent the condensation which causes the efficiency 
to fall below its possible level. In a gas engine, on the con- 
trary, the endeavour is to cool the cylinder to keep the engine 
from jamming and otherwise working badly. Clearly there 
is here a marked difference in operation, and correspondingly 
it becomes necessary to devise new standards of comparison 
suitable to the working of gas engines. 
There are Three Ideal Standard Cycles, viz. — 

1. The constant temperature type. 

2. The constant pressure type. 

3. The constant volume type. 

Each of these has been investigated by a Committee ap- 
pointed by the Institution of Civil Engineers, and as it is 
desirable to avoid a multiplicity of methods of dealing with 
the same thing, the author will follow generally the procedure 
they recommend. 

39. The Constant Temperature Type. — In an engine of 
this type, all the heat is taken in at the highest temperature 
and all is afterwards rejected at the lowest temperature. This 
is what has been defined above as the Carnot Cycle, and it can 
be proved that for the same temperature limits no possible 



32 THE INTERNAL COMBUSTION ENGINE [chap, ii 

treatment of a heat engine can give a higher efficiency than 
is theoretically obtainable in this way. The diagrams in Fig. 

T t 

11 show at once that the efficiency is — where Ti is the 

highest temperature and T the lowest, both of course 
being reckoned from the absolute zero of temperature. T 
is always used in this book to mean temperature absolute, 
and 6 to mean temperature as read on a thermometer. A PV 
diagram is also shown and any one acquainted with the working 
of steam or gas engines would recognize that for any given 
h.p. the cylinder would require to be exceedingly large and 



30 



20 



15 



Id 

a. 10 

CO 

CO 

u 
a 

B. 



Pf 




















1 










































1 






















1 
























































































\\ 


V P» 
























S P ~ 


















Bo 




^^ 


*v^~ 


^^ 










, 












r^ 








p« 

Pa 



3000 



hi 

-J25C! 
< 
U 
CO 

a 2000 

I 

< 

_ 

£ 1500 
< 

a. 

E 
uiooo 

t- 



500 



10 























































T; 


T-T* 




T# 




s 


/- 




« 


s 










To 





















VOLUME 



•i 
ENTROPY 



Fig. 11. 



costly, so that the extra economy in the matter of fuel 
brought about by its high efficiency would be more than 
counterbalanced by the inconvenience of the size of the 
engine and by the extra annual outlay necessary to pro- 
vide for interest and depreciation on the enhanced capital 
cost. 

No gas engine works on this cycle or indeed on anything 
very like it. It is not, therefore, quoted nearly so often in 
gas engine work as in steam engine practice. 



CHAP. II] 



THERMODYNAMIC CYCLES 



33 



40. The Constant Pressure Type. — In this type of engine all 
the heat is received at the highest pressure and rejected at 
the lowest pressure. 

T cp and PV diagrams are shown for this cycle in Fig. 12. 




2 5 

< 
z. 



a. c 



2500 



1500 



-<200C 

< 
(J 

a. 
i 
< 

(DI000 

< 

CL 

2 TV 

W 500- 









Tz 




























































/Ts 


















s\ 

































I 2 

ENTROPY 



Pz 





V 


X. 




■ 
























— 


- ■ 


















































_J — h^ 


































1 




~ 






1 v 3 


. 




1 IV 


1 i i i i i i 



10 
VOLUME. 



15 



Fig. 12. 



The heat received per lb. of gas in this case is (T 2 — T x ) X 
C p , and that rejected is (T 3 — T )XCp, so that 

heat taken in — heat rejected 



thermal efficiency: 



heat taken in 



=1 



T 3 -T 

t 2 -t; 



During the parts of the cycle shown by the lines T Ti and 
T 2 T 3 . heat is being neither received nor rejected by the gas ; 
the expansion and compression must therefore be adiabatic. 

n 



34 THE INTERNAL COMBUSTION ENGINE [chap, ii 
For adiabatic expansions, PV y — constant, and by par. 30 



py 

T 

Therefore — - 



-l 



^constant. 
P ^T and £=(£-• 



Thus 



T T 3 T 3 



y 



-To 



T x T 2 T 2 -T x 



Po 

Pi 



y 



/P \^ 
Therefore ^=1 — f — J v 



V /P, 



The compression ratio r=— -= 

» i 



Po 



Therefore ??— 1 — ( — J 



y 



= 1 



r 



This gives the value of the efficiency of this cycle in terms 
of r the compression ratio. It is an important fact that this 
efficiency is independent of the temperatures and pressures 
attained, and depends only on the ratio of compression. It 
shows that for high efficiencies the compression must be high. 



25 



2C 



— p i 1 



i*-V* ~H 



•5 
VOLUME 

_- Vc; -. 



2500 



I -10 




CNTROPY 



Fig. 13. 



chap, ii] THERMODYNAMIC CYCLES 35 

The Brayton and Diesel engines approach most nearly to this 
cycle. 

41. The Constant Volume Type. — In this type all the heat 
is received at constant volume and rejected also at constant 
volume. These two volumes are the volume at ignition and 
the volume at exhaust. This cycle may also be called the 
Otto or Beau de Rochas Cycle, and it is the one on which prac- 
tically all modern gas engines work or attempt to work. The 
diagrams in Fig. 13 show the working of the cycle. 

The efficiency is calculated in the same manner as the pre- 
vious one ; heat taken in =(T 2 — T^C,, and heat rejected 
= (T 3 — T )C„ 3 from which it follows that 

Efficiency = (I ^iA-tTa- TjC, 

(T.--T0C. 

'.-Tx-T.+To 



=1 

Then as before 



T 2 -T x 

T 3 -T 
T 2 -T x 



rT 



t; t 3 WJ 

( l V" 1 
Therefore r]=l — ( — ) 

And this it will be noted is exactly the same expression as 
before. Indeed,, the Carnot Cycle can also have its efficiency 
expressed in exactly the same way, but it must be remembered 
that although the efficiency of all three cycles depends upon 
the degree of compression and would be the same in all were 
the compression ratios the same, yet the temperature ranges 
would be very different, and it would be found that the Carnot 
Cycle gave the least range of tempe.ature for any given effi- 
ciency. The discovery that for the same compression ratios 
the same efficiency holds good for each of these three cycles is 
attributed to Professors Unwin and Callendar. 

In view of the simplicity of this result it is not difficult to 
understand that the Committee of the Institution of Civil 



36 THE INTERNAL COMBUSTION ENGINE [chap, ii 

Engineers, appointed to inquire into the matter, should have 
selected for use as the best expression for the ideal efficiency 
the form — 

This expression therefore holds the place in gas engine work 
which in the steam engine is filled by the well-known 

Tx-Tp 

42. The remaining point to be considered is the value to 
give to y. The gaseous mixture which works in gas engines 
depends upon whether lighting gas. producer gas. blast furnace 
gas or coke-oven gas is being employed, and with oil and petrol 
engines other mixtures occur. It is evidently impossible there- 
fore to get a value for y which will accurately suit all engines. 
It must be remembered, however, that the working fluid 
always consists chiefly of air. and it has been urged by some 
engineers that, having regard to the preponderance of the 
atmospheric oxygen and nitrogen in all internal combustion 
engines, little error could arise if it were all assumed to be air. 
The "Air Standard" for efficiency resulted. It assumes that 
air is the working fluid (and that the small quantity of com- 
bustible gas is merely used to heat this air by combustion), 
and that y has the air value of 1-40, so that 

--(f)" 

This expression gives for different values of r the following 
theoretical efficiencies — 



r 


* 


2 


0-242 


3 


0-356 


4 


0-426 


5 


0-475 


7 


0-541 


10 


0-602 


20 


0-698 


100 


0-841 



CHAP. II] 



THERMODYNAMIC CYCLES 



37 



In practice 50 to 60 per cent, of these efficiencies are usually 
obtained, and it is clear that a comparison between different 
engines can be made by noting what percentage of the ideal 
efficiency is obtained, in each case, for the compression ratio 
at which each works. A natural result of this rise of efficiency 



a: 



220 
























«- 




120- 


210 

(£200 
< 190 
2 180 
5,70 

|- 

(/> ISO 
O 140 

a 

j 130 
-.20 
°1.0 
x 100 
CD 90 
Z 80 

(0 70 

1- 

Z 60 










' 






I 


s. 1 




110- 
100- 

90- 






















*< 
47 


























£7 






W80- 




























U 


















T/ 1 






S 60 - 


















* 










Q 50- 

Z 
















( 


V 






t 




o 4o 

0. 












1 

1 J&/ 


°f 










30 


U 

z 50 

8 *° 

W 30 
S 20 






















OCLB. 


20 










S^ 






r^HTS^, 


OF <LB 


DRVAl 




& 


10 


X 

10 

o 

3C 




s. 


k=^B2 






1 wfT 


KT_COH] 
GHTOF 


S*rl*" 




1 






) 32 40 SO t/ ? 60 70 t SO 90 l60 110 120 130 1*0 15 

TEMPERATURE OF AIR ceht.o^de 

C 5 IO 15 20 25 30 35 40 45 50 55 60 6 

i x _ . i L ■ i ' 1 ' -J 1- 


0°FAHR. 

SCALE . 
5 70 



Fig. 14. — Curves showing heat contained in 1 lb. of saturated air at various 
temperatures. Thus tS represents the heat content of 1 lb. of dry air 
and the associated quantity of water vapour, which occupies the same 
volume as the 1 lb. of air at temperature t. 



with compression is that taken over a long range of years there 
has been a decided increase in compression pressures. It is 
indeed this movement which is the chief cause of the great 
advances that have been made in the heat economy of gas 
engines. Thus in 1880 a compression pressure of 30 or 40 lb. 
per sq. inch was usual. Now the compression pressure some- 
times goes up to 170 lb. per sq. inch when working with pro- 
ducer gas and with the Diesel oil engine as high as 500 lb. per 
sq. inch. The effect of high compression pressures is illus- 



38 THE INTERNAL COMBUSTION ENGINE [chap, ii 

trated in practice by the following comparative figures. It 
was found that an engine * working with a compression pres- 
sure of 120 lb. used 11,500 B.Th.U. per B.H.P.-hour, whereas 
one working with a corresponding pressure of 170 lb. used only 
9,500 B.Th.U. 

43. The Council of the Institution of Civil Engineers have 
permitted the reproduction of the diagrams in Figs. 11, 12 
and 13 from the Final Report f of the Committee on the Effi- 
ciency of Internal- Combustion Engines. They ako permitted 
the curve in Fig. 14 to be reproduced. It shows the heat con- 
tents for 1 lb. of air, and the associated quantity of water 
vapour. It therefore enables the observer to ascertain at 
once the heat contained in any weight of air at different tem- 
peratures. The ability to do this rapidly is very useful when 
a heat balance sheet is being made out for a gas engine run, 
and when considering the design of vaporisers for gas pro- 
ducers. 



EXAMPLES 

1. The mixture in a petrol-engine cylinder at atmospheric pressure 
and volume 1 is found to be at a temperature of 115° C. It is com- 
pressed and ignited. At a certain instant the pressure is 15 atmospheres 
and the volume 0-25. Find the temperature. [B. of E., 1910.] 

2. Dry air is pumped into a closed vessel of constant volume until 
the pressure inside it is 80 lb. per sq. inch by gauge ; the temperature 
is 90° F. What will be the pressure in the vessel after it has remained 
for a considerable time in a room where the temperature is 60° F. ? 

[Mech. Sc. Tripos, 1906.] 

3. Before compression, on a petrol engine diagram v = 10, p = 15, 
temperature = 150° C. At a point on the expansion part of the dia- 
gram where v = 4, p = 190, what is the temperature ? Assume that 
the mixture behaves as a perfect gas. [B. of E., 1911.] 

4. At the beginning of the compression part of the diagram of a gas- 
engine cylinder, the pressure is represented by a distance 0*31 in. and 
the volume by 3 in. The temperature is known to be 120° C. At a 
point on the expansion part of the diagram where the pressure is 7 in. 
and the volume 0-6 in., what is the temperature ? 

[B. of E., 1909.] 

* Mr. A. E. Porte in Proc. I.E.E., 1907. 
t I.C.E. Proc, Vols. 162 and 163. 



chap, ii] THERMODYNAMIC CYCLES 39 

5. One lb. of air has a volume of 4 cu. ft. and a pressure of 50 lb. 
per sq. inch ; the temperature is 127° C. It receives 250 C.H.U., its 
volume remaining constant. What is its new temperature and pres- 
sure ? The mean specific heat at constant volume may be taken as 
01 7. [B. of E., 1909.] 

6. A balloon of 5,000 cu. ft. capacity is to be so far filled with hydro- 
gen at a pressure of 30 inches of mercury and 15° C. that, after ascending 
to a height where the pressure is 20 inches of mercury and the tempera- 
ture 0° C, the silk envelope is then fully distended, no gas having been 
spilled. Calculate the mass of hydrogen required and its original 
volume. The density of hydrogen is 0-0056 lb. per cu. ft. at normal 
temperature and pressure. [Mech. Sc. Tripos, 1912.] 

7. Air at atmospheric pressure and at a temperature of 70° C. is con- 
tained in a cylinder of 2 cu. ft. volume, closed by a piston. The latter 
is forced down until the air is compressed into ^ cu. ft. Find its result- 
ing pressure (lb. per sq. inch) and temperature, if the compression is 
performed 

(a) Very slowly ; 

(b) Very quickly (i.e. so that heat has no time to escape) [y == 
1-41]. 

8. Assuming that the compression curve follows the law PV^ = con- 
stant [y = 1-4], calculate the pressure of the charge at the end of com- 
pression, given that the pressure at the beginning of the stroke is 12 
lb. per sq. inch abs. and that the final volume is i the initial volume. 

[B. of E., 1912.] 

9. A quantity of air at temperature 15° C. and pressure 25 lb. per 
sq. inch abs. is adiabatically compressed to one-half its volume. Find 
the resulting pressure and temperature. [Mech. Sc. Tripos, 1911.] 

10. Air at 68° F. and atmospheric pressure is compressed adiabatic- 
ally to 4 atmospheres. It is then cooled at constant volume in a receiver 
down to initial temperature, and then expanded in a non-conducting 
cylinder to atmospheric pressure. Find the highest and lowest 
temperatures. 

11. The ratio of compression in the cylinder of a Diesel oil engine 
is 15 : 1, and the temperature of the air at the end of the suction stroke 
is 70° C. Assume that the actual law of compression is PV 1,3 = con- 
stant, what is the temperature of the air at the end of compres- 
sion ? 

12. A vessel is exhausted of air to a pressure of 12 lb. per sq. inch 
abs., the pressure of the atmosphere being 15 lb. per sq. inch abs. The 
temperature of the whole being that of the atmosphere (60° F.), a cock 
is opened and air allowed to rush in until the pressure is equalized. 
Assuming that no heat is lost to the walls of the vessel, find the rise in 
temperature of the air within it. [Mech. Sc. Tripos, 1905.] 

13. If a quantity of gas expands isothermally from pressure P lb. 
per sq. ft., volume V cu. ft., to a place where the pressure and volume 



40 THE INTERNAL COMBUSTION ENGINE [chap, ii 

become Pi and V 1 respectively, show that the work done in ft. -lb. is 
given by 

2-3026 P V log 10 Xi- 

* 

14. A quantity of gas expands, the pressure (in lb. per sq. ft.) and 
volume (cu. ft.) being connected by the law PV* = constant. The 
initial pressure and volume being P and V and the final pressure and 
volume P t and V* show that the work done by the gas is 

F ° v °- p - v ' ft.-ib. 

n — 1 
Show also that the number of heat units received by the gas is 

PqVq-PiVi y-n 

J ■( 7 _i)( w _i) 

and hence show that if the curve PV" = constant lies below the adiabatic 
curve passing through the point (P , V ), the gas must be rejecting heat. 

15. A pound of air at atmospheric pressure and at 20° C. is to be 
compressed adiabatically to 10 atmospheres. Find the work done by 
the pump. The same result is arrived at by isothermal compression, 
cooling the air so that it keeps at 20° C, and when the pressure reaches 
10 atmospheres it is heated at constant pressure. Take the specific 
heats of air as 0-238 and 0-1694. State separately the work done upon 
and by the air, and the heat taken from and given to it, all in ft. -lb. 

16. A cartridge containing 4 lb. of air at 1,000 lb. per sq. inch (gauge 
pressure) and 15° C. is placed in the chamber of a gun behind a light 
frictionless piston fitting the bore of the gun. The cartridge is per- 
forated and the piston just reaches the muzzle of the gun. Calculate 
the final temperature of the air and the volume of the gun, on the 
assumption that the air absorbs no heat from the walls of the gun. 
[Atmospheric pressure = 14-7 lb. per sq. inch.] 

[Mech. Sc. Tripos, 1912.] 

17. A torpedo air-chamber contains initially 80 lb. of air at a pressure 
of 1,700 lb. per sq. inch abs. and 15° C, and at the end of the run the 
pressure is 500 lb. per sq. inch and the temperature 2° C. How much 
of the heat of the air which is left in the chamber has been abstracted 
from the sea ? [Mech. Sc. Tripos, 1911.] 

18. During the inflation of a balloon with hydrogen, the envelope 
breaks away when only i full. It rises in the air so quickly that there 
is no time for heat to enter or escape through the envelope. What 
will be the temperature of the hydrogen by the time it has expanded 
so as to fill completely the balloon, and what will be the barometric 
height of the altitude at which this occurs ? 

Temperature of H. on ground = 60° F. 
Barometric height on ground = 30 inches of mercury. 
Specific heat at constant pressure of H = 3-38. 
Specific heat at constant volume of H = 2-38. 



chap, ii] THERMODYNAMIC CYCLES 41 

19. A cubic foot of air at atmospheric pressure is compressed to 5 
atmospheres according to the lawPV 1-45 = constant. Initial tempera- 
ture = 59° F. 

Find— 

(i) Work done during compression. 
(ii) Heat received or rejected, 
(iii) Final temperature and volume. 

20. One pound of air is at 2 atmospheres and at a temperature of 
20° C. How many cu. ft. does it fill ? It receives heat energy equiva- 
lent to 100,000 ft. -lb., its volume remaining constant. Find the new 
temperature and pressure. The mean specific heat at constant volume 
of the air may be taken as 017. 

21. Liquid fuel is burnt in the air supply of a compressed air engine 
in the proportion of 1 lb. of fuel to 100 lb. of air, and the arrangements 
are such that the pressure is kept constant. Assuming that the calorific 
value of the liquid fuel is 20,000 B.Th.U.'s per lb. and that the specific 
heat at constant pressure of products of combustion is the same as 
that of air, viz., -238, what will be the temperature of the heated " air " 
entering the cylinder, if the temperature of air and fuel before com- 
bustion was 60° F. ? 

22. Air expands under a piston from a volume of 1 cu. ft. and 
pressure 300 lb. per sq. inch abs. to volume 5 cu. ft. and pressure 40 lb. 
per sq. inch abs. Assuming that the pressure and volume vary during 
the expansion according to the law PV n =constant, find the heat ab- 
sorbed in B.Th.U. 

23. A gas engine works with an ideal substance of constant specific 
heat, receiving and rejecting heat at constant volume and with adia- 
batic compression and expansion. The piston displacement per stroke 
is 1-2 cu. ft. and the clearance volume 0-15 cu. ft. Calculate the theo- 
retic thermal efficiency of the engine, taking y as 1-38. 

24. The cycle of operations in a gas-engine is as follows : — 

(1) Gas is compressed from V=3-76 cu. ft. to V=0-6 cu. ft. accord- 
ing to the law PV 1-i = 94-5. [P being the pressure in lb. per 
sq. inch.] 

(ii) On explosion, the pressure rises to 420 lb. per sq. inch, the volume 
remaining constant. 

(iii) Expansion takes place till V = 3-76 once more, the law followed 
being PV 1 ' 2 = constant. 

(iv) The pressure falls to its initial value, the volume remaining 3-76. 

Draw out the PV diagram from these data and find the mean 
effective pressure in lb. per sq. inch. 

25. A gas-engine works on an ideal cycle, with adiabatic compression 
and expansion, receiving and rejecting heat at constant volume. The 
piston displacement per stroke is 1 cu. ft., the clearance volume 02 
cu. ft., and at the beginning of compression the temperature of the 
cylinder contents is 600° F. absolute, the pressure being atmospheric. 
The engine receives 0-06 cu. ft. of gas per cycle (calorific value 600 
B.Th.U. per cu. ft.). Atmospheric pressure = 14-7 lb. per sq. inch. 



& IHE CSTEEXAL MBISTION EXGIXE Y ttap rr 



/ = 1-38] 

kcfcet loss and 



_- tt t — 

: "^eigiit :t i—ender lotti- 
fn| BreswiMe and. tesnjpeiatTir - 
__ re_=e it lete _t-te~tt- rimtg 

te^e ". . = : :r 
t~ r res stir e '■.' -it:: :. fXT-osteti 

_ tut: lertteire eitt tt---- re " end of expansion. 
h_ztt - . : ttte 

~~- t.tttitettt~ it • ... riigine ~ir.-ttr_^: itt t . etnot cycle between the 
same Mgiffiest and lowest temperatcr - 

3 Tripos, 190&1 



— -:e 



The 



: ; 



- tte ension was PV 1 '- = k 
tier of the heat was received 
tgtt - ; _ ltd lowest temperatures 
■ displacement was 2-8 cu. ft. 

Ttte ztttte,! ressiire was itmo- 



itt 

m 



'. *e - 

"1S~ rC 



y-ce 



pressiori and expansion, 
dnrrtti: -~,tt_ operation. 



_t^ itt en -t-_^ -it-- - _- itr-tt ir-ittt :e_f 
Esttre ts 1" tt -: inch. The inlet valve 

: tie rue tt itt etreeie ee t _ e^ trte-ttrf is tltett 
ii r : _:.-:- ~lte tettee _- — ire et tlte t tttte 
_= _ . eet - tnch below that of the atmo- 
ettee itti issmning that no heat passes 
z. 1 the tyiinder contents daring the suction 
ttte it tee tt i etned at external temperarare 
•treke is ' " tee lent, less than the stroke 
mr may be taken as 19-5 ft. -lb. per 
TvIecT So Tripos 1 -1 : ] 
• :t teentt tin the pressure in a 
ittle iir is teteg 'drawn from the re- 



. _ . 



:---_- ■ et :-: =tr< 
"wolinne. The- vofommefcrie lie: 
-~ in teen ee tt 

28s. A single-stage eounprei 

:-" -.--: ■■- '_ r v '~-_ ;.-: ;q - 

rt~er ' tee- ttte ~ : :t i 

= tt ~ :..\~ ittte i 

: etr it letiti-ee-tt 

lb. 

29L A bniMwn^ is to be bested by passing the air tor ventilating it 
-.it _.. "■ tt .--- i -.....■ tesses it ■: eabatically. then throttling 

it down to atmospheric pressoare on Leaving the compr - - - 1 r Hie tr 
titters ttte ie ttte tesse r t-t ' . -e: .- -- n t" _" . itt . i tete tti n 
air is SO lb. per mnsnte. Calculate the power requie e 1 - -timing unit 



inure and pressure = 13-1 eo. ft. 



~ i - . . - — et tettts " ■ - 1 - - kf. per k.w. - hour., com- 

. neee .. "". . -it bnrmtt. in a stove. 

tbe iron ebiimwwy of which passes t h i ough the air-doet and imparts 20 



chap, ii] THERMODYNAMIC CYCLES 43 

per cent, of the heat of combustion to the ventilating air. The cost of 
coal is Old. per lb. of calorific value 8,000 C.H.IT. per lb. 

[Mech. Sc. Tripos, 1911.] 

30. Air is compressed adiabatically into a receiver of V cu. ft. capacity 
to m times the atmospheric density. Show that, if P be the atmo- 
spheric pressure in lb. per sq. ft., the work expended is 

pv |-mr-w -| ft lb 

L y 1 J 

[Mech. Sc. Tripos, 1904.] 

31. Show that when a perfect gas is wire-drawn from one pressure 
to a lower one, without any gain of kinetic energy, the temperature is 
unaltered after expansion. 

32. In an ideal diagram of a Diesel engine, the gas is compressed 
adiabatically from volume V 1 to V 2 , then expands from volume V 2 to 
V 3 at constant pressure, further expands adiabatically from V 3 to V x 
and finally rejects heat at constant volume V t . Show that the thermal 
efficiencv may be expressed as 

ir *- 1 



i 



y(R-l) 

where r= — and K:= — 
v i V 2 



CHAPTER III 

Combustion and Explosion 

Chemical Combustion — Dugald Clerk's and Grover's Early 
Experiments on Explosion ln Closed Vessels — Discussion 
of Results — Increase of Specific Heats of Gases — Dissocia- 
tion — w * After -burning '* — Later Explosion Experiments — 
Time of Explosion — Turbulence — Gaseous Explosions Com- 
mittee. 

44. Chemical Combustion. — Instances of chemical com- 
bustion are manifold. Two among the commonest are the 
burning of coal, and the oxidation of the carbon in food which 
is the source of the heat energy given out by the human body. 
In place of coal, it is possible to burn gas made from coal and 
so obtain either heat or light. In a gas engine cylinder, gas 
and air are first mixed together and the whole mass ignited 
at once, so that the union is explosive. Useful figures to 
remember are that 1 lb. of coal on being burnt will liberate 
about 12, 000, GOO ft. -lb. of energy, a cubic foot of coal gas 
will liberate about 550,000 ft. -lb., 1 lb. of petroleum about 
18,000,000 ft.-lb., and 1 lb. of petrol some 15,000,000 ft.-lb. 
These are very large amounts, and were it possible to invent 
a heat engine of 100 per cent, efficiency it is plain that a very 
liberal supply of energy would be obtainable at little cost. 
With existing engines 1 lb. of coal with potential energy equal 
to 12,000,000 ft.-lb. will only give in energy on the brake 
about 3,000,000 ft.-lb. with the best steam engines and 4,000,000 
ft.-lb. with the best gas engines, the waste energy being 9,000,000 
ft.-lb. and 8,000,000 ft.-lb. respectively in the two cases. 

The loss of 8,000,000 ft.-lb. which occurs in a gas engine 
is divided between the loss to the water in the cooling jacket 
and the loss which occurs owing to the exhaust products 

44 



chap, in] COMBUSTION AND EXPLOSION 



45 



being at a high temperature and so carrying off a large unutil- 
ized portion of the heat. The loss to the cylinder walls is the 
more difficult to follow in all the intricacies of the working 
cycle. The cooling jacket is necessary,* as without it the 
piston and cylinder would get almost red hot and the engine 
would stop running. The temperature-flow through the 
metal depends on the position of the piston in its stroke, but 
it is difficult to determine the precise relationship. 

45. If ; after a charge of gas and air has been drawn into 
a gas engine cylinder, the flywheel be held so that it cannot 
move and the charge be then ignited, a rapid rise of pressure 
is recorded on the indicator. It ought, one might think, to 
be easy to calculate what this rise would be, since the quantity 
of gas and air admitted and their quality are easily deter- 
minable and the amount of thermal energy liberated is there- 
fore known. If this amount of energy be divided by the 
amount of heat required to heat the mixture through one 
degree Cent, it is clear that the resulting temperature would 

PV 

be ascertained, and from this it would be simple by the — law 

to determine the, resulting pressure. This had often been 
done, but it had always been found that the pressure actually 
obtained was only about one-half that calculated. Here are 
the actual figures obtained in some experiments carried out 
many years ago by Dugald Clerk — 



Ratio air /gas 


Absolute Pressure 
Obtained 


Absolute Pressure 
Calculated 




lb. 


per sq. inch 


lb. per sq. inch 


14 




55 


110 


13 




661 


116 


12 




75 


123 


11 




76 


132 


9 




93 


161 


7 




102 


193 


6 




105 


214 


5 




106 


206 


4 




95 


196 



Except in very small cylinders, which are sometimes air cooled. 



THE INTERNAL COMBUSTION ENGINE [chap, hi 

On an average there appears here to be a loss of as much 
- 5 per cent, of the pressure. Why is this 
46. Several explanations have been put forward to account 
for this loss. The most important are — 

1. The Dissociation Theory. — It is well known that chemical 
compounds such as H 2 or CO, dissociate at high temperatures 
into simpler gases and in so doing absorb heat. It has there- 
fore been thought that at the high temperatures of explosion 
such dissociation would occur and the heat so absorbed might 
account for the missing 50 per cent. This assumption, how- 
ever, involves the deduction that for weak explosions, in which 
low pressures and temperatures were attained, the effect should 
be much less, so that the actual pressure would form a much 
larger proportion of the calculated pressure, and the converse 
in the case of rich mixtures. As a glance at the above figures 
will show. this, however, is not the case ; at the weakest 
mixture of 1 to 14 the missing pressure is 50 per cent., and 
at the richest of 4 to 1 it is 52 per cent., or practically the same 
This theory alone therefore does not suffice to account for 
the observed facte 

2. Hut Cooling Theory. — This assumes that the cooling 
effect of the cylinder walls is so great that the pressure actually 
obtained must fall much below the ideal calculated. It 
does not explain, however, why the loss should be always 
50 per cent, in the particular cylinder used. nor ; moreover. 
does it explain why a 50 per cent, loss is found still to occur 
even when a cylinder of a different size and shape is chosen. 
v : that this theory also is inadequate in itself to explain the 
observed effect. 

3. The Increasing Specific Heat Theory. — This is the theory 
advanced first by MM. Mallard and Le Chatelier. who found 
as the result of their experiments that the specific heat of gases 
and particularly of C0 2 appeared to increase considerably 
with rise of temperature. The objection commonly alleged 
against this theory is that, as in the Dissociation Theory, it 
requires that a greater proportion of the ideal pressure should 
be obtained at lower temperatures than at higher, and that 
this is not found to be the case. 

4. The After-burning Theory. — This theory has chiefly 



chap, in] COMBUSTION AND EXPLOSION 47 

been associated with the name of Dugald Clerk, who sug- 
gested that the combustion of the gas was not as rapid as 
supposed and that not all the heat was liberated before the 
moment of highest pressure. It assumed in fact that the 
gas was still burning long after the point of maximum pressure 
and that the cooling effect of the walls had therefore a much 
longer time to operate than had been generally supposed. 
In an actual gas engine this would mean that the gas would 
be burning right through the working stroke, and that it must 
sometimes happen that unburnt gas would pass away in the 
exhaust. The objection to this theory lies in the fact that 
it has never been shown conclusively that the explosion is 
not complete at the point of highest temperature. Indeed 
the evidence is rather the other way. It is not usual to find 
that the exhaust contain: more than a very few per cent, of 
unburnt gases, and it has moreover been shown that a com- 
plete heat balance analysis can be obtained without the need 
of any such hypothesis. 

47. Thus there are four simple theories, of which none 
appear to be sufficient in themselves to account for the observed 
loss. The difficulty is so fundamental a one that still further 
theories compounded of the above have been put forward. 
Dugald Clerk made the suggestion, as will be explained later 
at greater length, that the " suppressed " 50 per cent, may be 
accounted for on the supposition that part is due to the after- 
burning loss and part to a certain increase in specific heats. 
The author has seen no reason to modify the suggestion he 
put forward at the meeting of the British Association * in 
1902, viz. that the so-called " suppression of temperature " 
is probably due to the combined action of cooling and of 
increase of specific heat on the lines suggested by the French 
physicists, MM. Mallard and Le Chatelier. Although the 
increase of specific heat left a larger proportion of loss to be 
accounted for at low temperatures than at high ones, this 
was sufficiently explained by the fact that the ignition period 
was much longer at low temperatures and so allowed the cool- 
ing effect to have a longer time for action than it would have 

* The Engineer, October 10, 1902 ; Engineering, October 10, 1902. 



48 THE INTERNAL COMBUSTION ENGINE [chap, hi 

at high temperatures. This meant that for weak mixtures 
the 50 per cent, loss was mainly due to cooling, for rich mixtures 
mainly due to increase of specific heat, and for intermediate 
mixtures was due to a combination of the two. 

Dugald Clerk's early experiments consisted in indicating 
explosions of mixtures of air with Glasgow and Oldham gas 
in a closed cylinder 7 in. by 8J in. The indicator registered 
pressure p on a rotating drum driven at a known constant 
speed, so that curves were obtained showing the relation 
between p (pressure) and t (time) during the explosion and the 
subsequent cooling of the gas to the walls and ends of the 
cylinder. From the diagrams so obtained it was of course 
possible to measure the time occupied by the explosion, and 
the subsequent rate of fall of pressure due to cooling. At the 
time these experiments were made the specific heat was thought 
to be constant and it is important to note how greatly its 
now known increase with temperature affects the calculated 
pressures, particularly if for the moment MM. Mallard and 
Le Chateliers figures be adopted. That there are objections 
to the method of experimenting by which the French physicists 
obtained their results is well known. In fact Prof. Callendar 
has remarked : " The method of experiment employed was 
closely analogous to the explosion that was taking place in 
the gas engine itself. Explosive mixtures were fixed in a 
closed cylinder 17 in. by 7 in., and the maximum pressure 
was read by means of a Bourdon gauge." Since the date of 
their experiments other measurements have been made, and 
these will in due course be discussed ; but the increase of 
specific heat with temperature is undoubted, and for the 
present purpose MM. Mallard and Le Cha teller's figures are 
taken as illustrative. If the theoretical temperature of 
explosion is calculated from these values the difference from 
the observed value is much less. Thus a column may now 
be added to the table last given and the results are also shown 
in Fig. 15. 

It will be seen that in the case of the weakest mixture the 
50 per cent, loss has been reduced to 34 per cent., and in the 
case of the richest 52 per cent, has been reduced to 23 per cent., 
showing a step in the required direction. The balance is 






chap, in] COMBUSTION AND EXPLOSION 



49 







Absolute Pressure 


Absolute Pressure 


Ratio air /gas 


Absolute Pressure 
Obtained 


Calculated on 
Constant 


Calculated on 
Variable 






Specific Heat 


Specific Heat 


14 


55 


110 


83 


13 


661 


116 


86 


12 


75 


123 


90| 


11 


76 


132 


95 


9 


93 


161 


107 


7 


102 


190 


121 


6 


105 


214 


131 


5 


106 


206 


127 


4 


95 


196 


123 



taken to be made up of convection and radiation losses. The 
convection loss to the cold walls of the containing vessel 



250 



200 



'/SO 



100 



lb) 



50 



Maximum Pressures obtained on 
explosfon in a closed vessel of diF- 
-Ferent mixtures oF coal gas and air 




G 8 10 

Ratio Air/ 6 as. 

Curve A : Maximum pressure on Const '. Sp: Neat Hypothesis. 

CurveB: " " » Var: " " " 



Points marked O are Dugald Clerk's Results. 

Fig. 15. 




E 



THE INTERNAL COMBUSTION ENGINE [chap, m 

take? place at all temperatures : the radiation loss on the 
other hand is important only at the moments of highr-": 
temperature. Prof. Hopkinson has shown that the cooling 
losses depend also on the state of the inner surface of the 
vessel, whether bright or blackened. 

The law of cooling of gaseous mixtures enclosed in metal 
cylinders of stated dimensions is not easy to apply to the c 
of ordinary gas engines. First, because the connexion between 
the rate of loss of heat and the dimensions of the cylinder is 
very complicated, but even more because in an ordinary gas 
engine cylinder the temperature of the cylinder walls and of 
the piston are so very different that conditions sometimes 
arise in which while the gas is being heated by the piston it is 
at the same time being cooled by the cylinder walls, a condi- 
tion of affairs in no way analogous to that holding in the ab : vc 
experiments. 

48. Graver's Explosion Experiments. — At the time these 
calculations were made the only other well-known experi- 
ments upon the explosion of gases in closed vessels were those 
of Grover. and at the British Association meeting in 1903 
an endeavour was made to show how far the combined variable 
specific heat and cooling theory would go towards explaining 
the very remarkable results obtained by Grover. which in no 
way resembled those obtained by Dugald Clerk, inasmuch 
as the former found much lower pressures and came to the 
unexpected conclusion that the retention of waste products 
in a gas engine cylinder increased the pressure of the ensuing 
explosion, an astonishing result having regard to the great care 
taken by most gas engine manufacturers to sweep out the 
greatest possible amount of the products of old explosions. 
The great difference between the ma x imum pressures obtained 
by Dugald Clerk and Grover is illustrated in Fig. 16. 

It was Grover *s idea not only to measure the pressures 
produced by various richnesses of mixture of coal-gas and 
air. but to investigate whether the resultant pressure on 
explosion was affected by replacing the air in excess of 
that calculated as chemically necessary for complete com- 
bustion by a portion of the burnt products of the previous 
explosion. Now it appears from Grover's account of the 



chap, in] COMBUSTION AND EXPLOSION 51 

experiments that he had an iron cylinder of one cubic foot 
capacity, and that in each series of experiments the volume 
of the coal gas admitted was kept constant and the cylinder 
was then filled with a mixture of air and waste products in 
various proportions. This was done in each series by filling 
the cylinder with water, and allowing gas to enter whilst a 
known volume of water was run out. Thus after an explosion 
water was allowed to pass into the cylinder until all but the 
required volume of burnt products had been forced out ; so 
that if it were desired that no burnt products should be left, 
the cylinder would be completely filled with water, but if, say, 
50 per cent, of the volume of the cylinder was required to 
contain burnt products, the water would only be permitted 
to rise half-way up the cylinder. 

The pressure was recorded in the customary manner on 
a rotating drum, but very few of the curves are given in the 
published account of the experiments, and it is therefore 
difficult to make a very exact comparison between the time 
rate of fall of the pressure after explosion in Grover's experi- 
ments (using, of course, those experiments in which no burnt 
products were admitted) with those of Dugald Clerk. 
However, so far as the curves can be examined, they show for 
the same pressures almost exactly the same rate of fall, a result 
which is the less unexpected, as the diameters of the two 
cylinders appear to have been nearly equal. It is not difficult 
to calculate what the ideal maximum temperature and corre- 
sponding pressure of explosion would be, using the same 
variable specific heat figures, and assuming no cooling of 
the gas by the walls, and when this has been done, it may be 
compared with the pressure found experimentally. The 
following table (see page 52) shows the result of such a cal- 
culation. 

In this table there is also given the difference in the heat 
energy between the gas at this temperature and at the actual 
temperature attained. 

The curves (p. 52) show the actual pressures plotted with 
respect to richness of mixture for the experiments of both 
investigators. It is seen that Grover's curve lies far below 
Dugald Clerk's. This cannot be due entirely to the different 



52 



THE INTERNAL COMBUSTION ENGINE "chap, m 



Ratio of Air 
to G . 


Observed 




^ir:r: A;:;::::c. 


15 


(AbsoL) 
31 


(AbsoL) 




Fr.-Ib. 
21.000 


14 


39 


"• 




19,000 


13 


- 


79 




18,000 


12 


51 


V:. 




: s. •:■■".'■■ 


10 


63 


92 




18 T 000 


- 


" 


104 




!*..;.,;,;, 


6 


11 


119 




31.000 



cylinder volumes used (317 and 1.728 cubic inches), or tc 
differences in the chemical constitution of the gases, becav 
as will be seen from the intermediate curve, there is little 



Max imam pressures obtained 







7 9 Mf II 2 12 14 

J: - 16. — Explosion curves showing much lower pressures btained by 
Grover than by other observe : 

disagreement between the results obtained by Dogald Clerk 
and by Douglas, although the results * obtained by the latter 
were for gases enclosed, not in iron cylinders, but in a eudio- 

*See27 V t, April 22. LSST nd November 7, 1! - 



chap, in] COMBUSTION AND EXPLOSION 53 

meter tube. If the use of a eudiometer does not produce 
results more different from Dugald Clerk's than this, the pre 
sumption certainly is that some factor must have entered 
iuto Grover's experiments which has entirely masked his 
results. A suggestion as to what this factor could be has been 
made by Grover himself, for in describing one experiment 
he says : " The difference is no doubt due to the fact that 
water was present on the walls of the cylinder " ; but Grover 
did not consider apparently that this presence of water affected 
his conclusions on the subject generally — conclusions which 
are set forth in his Modern Gas and Oil Engines. 

There is, of course, a limit to the quantity of water which 
could adhere to the walls of the cylinder, and it is necessary 
to see whether the required amount is what could reasonably 
be expected to exist. The average loss of energy given in 
column 4 of the table on p. 52 is about 20,000 ft. -lb , 
and considering the average energy given to 1 lb. of water 
to raise it from atmospheric temperature to superheated 
steam at the average maximum temperature, as about 750 
Cent, heat units, it follows that the weight of water required 
equals 0-0191 lb. This would occupy a space of about 0-53 
cubic inch, and in a cylinder of the dimensions used a film of 
water ^^jgin. thick would be sufficient to account for this. So 
that there is no difficulty in accounting for the presence of a 
sufficient quantity of water. To show the result of the pre- 
sence of water a simple example may be taken, in which the 
weight of the water film is three-eighths of the weight of the 
gaseous mixture, and in which both continue at the same 
temperature and pressure. When the pressure (absolute) 
amounted to 33 lb. per square inch, a calculation made in 
the absence of the knowledge of the presence of a water 
film would give a temperature of 254° Cent., whereas the 
real temperature would be 124° Cent., a very different result. 
A further calculation with the same amount of water present 
shows that a pressure of 60 lb. per square inch would be attained 
on explosion, whereas under the same circumstances, but 
in the absence of the water film, a pressure of 100 lb. per squaie 
inch would have been attained. 

It may be concluded that the presence of a water film of 



54 THE INTERNAL COMBUSTION EXGIXE [chap, hi 

varying extent is a sufficient explanation of the very curious 
results obtained by Grover. 

49. Later Experiments. — In addition to the early experi- 
ments of Dugalcl Clerk and Grover, some work in the same 
direction was done at the Massachusetts Institute of Tech- 
nology, but it does not appear that any definite conclusions 
were drawn therefrom. Later experiments have been made 
by Dugald Clerk. Hopkinson. and Bairstow and Alexander 
at the Royal College of Science. Taking the last first : 
Bairstow and Alexander's experiments were made on mixtures 
of London coal gas and air in a cylinder 18 in. long and 10 in. 
in diameter, pressures were indicated on a rotating drum, 
and the results of the investigations were communicated to 
the Southport meeting of the British Association in 1903. and 
to the Royal Society two years later. The chief interest of 
these tests lies in the fact that various initial pressures were 
used, instead of the atmospheric initial pressure used by 
earlier experimenters. The following table gives a selection 
from their results — 

Royal College oe Science Experiments. Explosions ix 
Closed Vessel ; Yapioes Ixltial Ppessepes and two Mlxtepe 

Strengths. 



Mixture 



Air Gas 



Initial 




Max. Press. 


Time to 


Pressure 


Initial 


observed 


reach this 


lb. per 


Temp. 


lb. per 


pressure . 


sq. in. 


-c. 


sq. m. 


sees. 


abs. 




abs. 





0-169 *4-8 23-5 348 0042 

0172 34-5 22 270 0041 





1 


01 70 


24-7 • 


21 


189 


0041 




1 


0168 


14-55 


21 


112 


0036 




1 1 


0-166 


9-71 


24-5 


68 


005 




1 1 


U-166 


7-18 


24 


47 


0-10 




(1 


0103 


44-7 


16-5 


238 


0-33 




0105 


34-6 


18-6 


185 


0-35 




1 


0104 


24-7 


20-0 


126 


0-41 




( 1 


0107 


14-4 


21-0 


74 


0-44 




1 1 


104 


9-5 


21-5 


46 


0-50 




1 1 


0-107 


7-06 


22-0 


33 


0-50 



chap, in] COMBUSTION AND EXPLOSION 



55 



Details of these experiments will be found in Dugald 
Clerk's book on The Gas Engine, Vol. I. It is left as an 
exercise to students to compare these explosion pressures 
with those theoretically obtainable, taking the Gaseous Explo- 
sions Committee's figures for specific heats. 

50. Time of Explosion. — In 1900 Dugald Clerk measured 
the time occupied in the explosion of coal gas and air 
from the moment of ignition to that of maximum pressure. 
The following were some of the times for various ratios of 
air to gas. 



Volumes of air to one 
volume of gas 



Time of explosion 



11 


0-290 sec. 


9 


0-155 „ 


7 


0-067 „ 


6 


0055 „ 



These figures were obtained from explosion experiments in 
closed vessels in which the mixture before explosion was at 




Fig. 17. — Indicator diagrams showing effect of Turbulence. A B is explosion 
curve when charge is fired on first compression stroke ; duration of 
explosion 0*037 second. C D is explosion when charge is fired upon the 
third compression ; duration of explosion 0-092 second. 



rest. They may be compared with those in the table on 
p. 54. When the mixture is turbulent the time of explosion is 



5€ THE INTERNAL . ; MBUSTION ENGINE ;chap. ni 

very much, shorter. In a working gas engine for instance the 
times of explosion are much less than any of the above figure - 
Indeed did the explosion take as long as in the above table, the 
working of the engine would be quite impossible. A small gas 
engine can be made to run at 600 r.p.m. so that each stroke 
occupies only 0-05 sec. and the explosion is usually : impleted 
in quite a small fraction of the stroke, which shows how much 
more rapid the explosion must be when there is ~\:z~:ulence. 




1\r LS — Professor Hopkmson? >?.- Explosion. Apps 



7„t effect of turbulence is well shown in Fig. 17. which is 
reproduced from some indicator cards taken by Dugald Clerk. 
In the one case we have the normal diagram produced by 
normal ignition arrangements, whilst in the other the turbu- 
lence which the gaseous mixture had during the suction 
stroke has intentionally been given time to die down before 
the spark is passed. The effect of this delay is -ren in the 
changed diagram,, which illustrates clearly the continuance 




chap, in] COMBUSTION AND EXPLOSION 



57 



of combustion throughout the whole length of the expansion 
stroke. 

51. Hopkinson. — A series of explosion experiments was 
undertaken by Prof. Hopkinson and communicated to the 
Royal Society in 1906. The vessel is shown in Fig. 18. A 
is the sparking point, B, C and D are platinum thermo- 
meters. Thermometer B is practically at the centre of the 
vessel. C is about 30 cm. distant from the spark and D is about 
1 cm. from the walls of the vessel. A record of the pressure 
was taken on the same drum as that upon which the tem- 
peratures were electrically recorded. The indicator* was 
very simple, consisting as it did of a piston controlled by a 
flat steel spring held at the two ends. As the spring w T as 
deflected a mirror tilted and so threw a beam of light on to 
the moving film. The period of the instrument was about 
sI-q sec. Fig. 19 shows the result obtained in the form of a 
graph. The following table serves also to show the actual 
indications recorded by the electric thermometer placed at 
the centre of the vessel : — 



Time 


Resistance 


Rise of Resistance 


Temperature in 


Sees. 


Ohms 


Ohms 


Degrees C. 


0-008 


2205 


12-4 


560 


0024 


30-3 


20-7 


995 


0041 


32-7 


231 


1,135 


0057 


331 


23-5 


1,165 


0074 


331 


23-5 


1,165 


0-09 


340 


24-4 


1,225 


0-107 


34-5 


24-9 


1,260 


0123 


34-7 


251 


1,275 


0140 


34-7 


251 


1,275 


0173 


36-6 


27-0 


1,400 


0-26 


wire melts 


— 


1,710 



An investigation had also to be made into the question of 
the existence of a time and temperature lag in the temperature 
recorded by the thin platinum wire. Prof. Hopkinson found 
the temperature of the wire to lag materially behind that 
of the gas when the latter was changing rapidly. To measure 
this, wires of two different thicknesses were used, viz. 

* See Fig. 40. 



1000 



58 THE INTERNAL COMBUSTION ENGINE [chap, m 



in. and -ott^jj in. respectively, and by a comparison of the 
results obtained Prof. Hopkinson was able to find the amount 
of the correction which he considered it necessary to employ. 
The most important of the conclusions reached by this 
experimenter, who. he tells his readers, carried out these 
experiments, largely '* with the object of finding the cause 
of the so-called ' suppression of heat " in explosions," is that 
his experiments appear to prove that even in the weakest 
mixture*, combustion, when once initiated at any point, is almost 



2 s: f 







Q-3 Sees. 



instantaneously complete. Moreover, he adds, they show 
that the specific heat of the products is very much greater at 
high temperatures than at low. and the extent of the difference 
seems to justify the view that it is the main reason of the so- 
called "''suppression of heat.'* 

52. In addition to these conclusions Prof. Hopkinson found 
certain differences in the temperature of the gas in different 
parts of the vessel, and this supports the results obtained by 
Prof. Burstall in his gas engine trials for the Institution of 
Mechanical Engineers. In experimenting with a rich mixture 



chap, in] COMBUSTION AND EXPLOSION 59 

(air gas = 9) Professor Hopkinson found that at the moment 
of maximum pressure the distribution of temperature in his 
vessel was roughly as follows — 

Mean temperature (inferred from pressure) . 1,600° C. 

(a) Centre near spark . . . . 1,900° C. 

(b) 10 cm. within the wall (C, Fig. 11) . . 1,700° C. 

(c) 1 cm. from wall at end (D, Fig. 11) 1,000 tol,300°C. 

(d) 1 cm. from wall at side .... 850° C. 

It is explained that " at points a, b and c the gases can 
have lost but little heat at this time, and the differences of 
temperature are almost wholly due to the different treatment 
of the gas at different places. At (a) it has been burnt nearly 
at atmospheric pressure, and compressed after burning 
to about 6J atmospheres absolute, while at (c) it has been 
first compressed to about six atmospheres as in a gas engine, 
and then ignited without any subsequent compression. At 
the point (d) much heat has been lost, since this is the first 
point on the wall reached by the flame ; the gas here is ignited 
when the pressure is' about two atmospheres, its temperature 
rises instantly to 1,300° C. and at once begins to fall." 

In experiments on a weak mixture of twelve volumes of 
air to one of gas the explosion was affected very greatly by 
the convection current set up, owing to the ignited gas being 
lighter and rising through the vessel. In the rich mixture 
this could not happen to the same extent, as the maximum 
pressure was reached about a quarter of a second after firing, 
whilst with the weak mixture the interval was two and a half 
seconds and so the time for convection was much longer. 
The experimenter recorded that " a few centimetres below 
the spark the temperature will rise rapidly and then fall ; 
the flame reaches the wire, and is then carried upward and 
away from it, the wire being cooled by the current of cold, 
unburnt gas which follows in the wake of the ascending flame. 
About one second after ignition, and while the pressure is 
still less than 10 lb. above atmosphere, the upper part of 
the vessel is filled with burnt gas which is in contact with, 
and losing heat to, the upper half of the walls." The lower 
half of the gas is therefore burnt last. Finally it may be 
recorded that Professor Hopkinson in comparing the behaviour 



60 THE INTERNAL COMBUSTION ENGINE chap, hi 

of rich and poor mixtures says : " It is safe to assume in 
dealing with a 12 1 mixture that one-fifth of a second after 
maximum pressure (when the loss of pressure by cooling is 
still less than 5 per cent.) there is present in the cylinder a 
mass of C0 2 . H 2 0. and inert gas in complete chemical equili- 
brium. In the 9 1 mixture this state is. of course, attained 
very much sooner. The difference in the behaviour of the weak 
and strong mixtures is wholly due to the very slow propa- 
gation of flame in the former : in a 9 1 mixture the flame 
seems to travel about ten times as fast as in the 12 1 mixture."" 

Professor Hopkinson has also measured the temperature 
of the air in a cylinder when the engine is turned by an electric 
motor. The air is then compressed and expanded almost 
adiabatically. It was found that at the top of compression 
the temperature of the air half a centimetre from the wall was 
some 30 deg. Cent, less than it was in the centre. At points 
nearer the wall, that is, within 1 mm. the temperature fell 
off very rapidly — although still materially above that of the 
wall face even at a distance from it of only y 1 - mm. 

53. The "Zig-Zag" Experiments.— In 1906 Dugald Clerk 
communicated to the Royal Society the results of some explo- 
sion experiments he had made by a new method to determine 
the volumetric heat of the gaseous mixture used in the gas 
engine. According to that description this consisted in 
running a gas engine under the ordinary standard conditions. 
and then at a given moment preventing the exhaust and 
inlet valves from opening, and at the same time taking a series 
of indicator diagrams. These diagrams showed a number 
of expansion and compression curves with the pressures 
gradually falling as the gas cooled. Fig. 20 is a representation 
of a series of curves so obtained. From the shape of such 
curves it is possible to calculate what is occurring to the 
gas in the cylinder. The following explanation of the method 
is given in the First Report of the B. A. Gaseous Explosions 
Committee : " The calculation is based on the assumption 
that the total heat loss from the hot gases during any given 
portion of a stroke is the same in expansion and compression 
if the mean temperature be the same. In the first compression 
the temperature of the gas rose to about 1100 : C. fat the 



chap, in] COMBUSTION AND EXPLOSION 



61 



point C. Fig. 20). During the first three-tenths of the following 
expansion stroke (CD), the temperature fell to about 700° C. 
The work done in this part of the expansion was measured 
and the heat loss determined as above was added. Thus the 
change of internal energy corresponding to the temperature 
change 1100° — 700° is obtained. The average volumetric 




Fig. 20.— Dugald Clerk's 



1/9 mixture. 



heat over this range is within the errors of experiment equal 
to the volumetric heat at the mean temperature of 900° C, 
which accordingly is by this method determined direct instead 
of by difference, as is necessarily the case when (as in some 
other experiments) the whole internal energy change associated 
with complete cooling of the gas is measured." 

The volumetric heat figures thus found by Clerk are given 
in the following tables. 

Volumetric Heat (Instantaneous) of Working Fluid. 



Temperature 


Volumetric Heat 


Temperature 


Volumetric Heat 


Degrees C. 


Ft. -lb. 


Degrees C. 


Ft.-lb. 





19-6 


800 


26-2 


100 


20-9 


900 


26-6 


200 


220 


1,000 


26-8 


300 


230 


1,100 


27-0 


400 


23-9 


1,200 


27-2 


500 


24-8 


1,300 


27-3 


600 


25-2 


1,400 


27-35 


700 


25-7 


1,500 


27-45 



62 THE INTERNAL COMBUSTION ENGINE [chap, hi 



Mean Volumetric Heat of Working Fluid over Temperature 

Range shown 



Temperature 


Volumetric Heat 


Temperature 


Volumetric Heat 


Degrees C. 


Ft. -lb. 


Degrees C. 


Ft. -lb. 


0—100 


20-3 


0—900 


23-9 


0—200 


20-9 


0—1. COO 


241 


0—300 


21-4 


0—1.100 


24-4 


0—400 


21-9 


0—1,200 


24-6 


0—500 


22-4 


0—1,300 


24-8 


0—600 


22-8 


0—1.400 


250 


0—700 


23-2 


0—1.500 


25-2 


0—800 


23-6 


— 


— 



It will be observed from the above that although the appar- 
ent specific heat was found to increase with rise of temperature . 
it tended towards a limiting value. The increase found for 
the first 500° C. was far more than for the last £00 \ This 
conclusion does not quite accord with the experiments of 
other workers. 

54. Gaseous Explosions Committee. — This Committee was 
appointed by the British Association in 1907 "for the Inves- 
tigation of Gaseous Explosions, with special reference to Tem- 
perature." No other work has thrown so much light upon the 
theory of the internal combustion engine as have the labours 
of this Committee. One of the first tasks undertaken was a 
thorough sifting of the experimental work bearing on the rise 
of specific heat of gases with temperature. This experimental 
work was divided into three classes : — 

(1) Constant-pressure experiments : Regnault. Wiedemann, 
Witkowski. Lussana, Holbom and Austin. Holborn and Hen- 
ning. The gas is heated from an external source in these 
experiments, and is at atmospheric pressure. 

(2) Experiments in which both volume and pressure are 
varied, the gas being heated by compression. The above 
mentioned experiments of Clerk and the determinations of the 
velocity of sound in hot gas by Dixon and others belong to 
this class. 

(3) Constant-volume experiment. To this category belong 









chap, in] COMBUSTION AND EXPLOSION 



63 



the explosion experiments of Mallard and Le Chatelier, Clerk, 
Langen, Petavel, Hopkinson, and others, and Joly's deter- 
minations with the steam calorimeter. In the explosion ex- 
periments the gas is heated by internal combustion. 

As a result of a full examination of this large mass of experi- 
mental work the Committee published a curve of internal 
energy at various temperatures for the gas engine mixture 
with which Clerk had experimented (Air/Gas — 9/1), and this 




500 1000 1500 

Temperature , Centigrade. 



2000 



Fig. 21. — Specific Heat, and Volumetric Heat, of expanding Gases in a 
Gas Engine at different Temperatures. 



curve in slightly modified form is reproduced in Fig. 25, on 
p. 84. 

The tangent at any point of this curve is a measure of the 
specific heat at that point, and it is found that the following 
linear equation represents the specific heat within the limits 
of experimental accuracy 

C, =0-152 +0-000075 T 

or in other units 

Volumetric heat = 16-6 + 0-0082 T in ft.-lb. per cubic 
foot. 

This is illustrated in Fig. 21, 



64 THE INTERNAL COMBUSTION ENGINE [chap, hi 

The following table gives the values of specific heat and 
volumetric heat for the temperatures named. 



Temperature 


Cv 


Volumetric heats 


Deg. Cent. 




Ft. -lb. per standard cu. ft. 


250 


0-19 


21 


750 


0-23 


25 


1250 


0-27 


29 


1750 


0-30 


33 



Although these values refer to the expanding gases in a gas 
engine, they may also be applied with approximately correct 
results to the gaseous mixture before explosion. Using this 
table it is possible therefore to estimate temperature rises 
corresponding to various amounts of heat energy supplied. 
The temperatures so estimated will, of course, only be approxi- 
mately correct, unless the temperature range happened to be 
centred around one of the above temperatures. It is in: 
teresting to compare this table with that on p. 61. 



EXAMPLE 

1. A mixture of coal-gas and air containing 10 per cent, of coal-gas is 
fired in a large spherical vessel by a spark at the centre, and the tem- 
perature of the gas is recorded by platinum thermometers, one of which 




c/ 1 

/ IB 




Tenths of a Second 

(A) is placed close to the spark and the other (B) near to the walls of 
the vessel. The records of temperature (curves A and B) and the 
simultaneous record of pressure (curve C) are shown in the figure. The 



chai*. in] COMBUSTION AND EXPLOSION 



65 



records start from the moment of firing. Explain the characteristic 
features of the temperature records, particularly the rise which occurs 
in A after 01 sees, and the slow rise in B during the first two -tenths of 
a second. 

Estimate from record A the volumetric heat of the products of 
combustion over the range 1200° to 1800° C. 

[Mech. Sc. Tripos, 1913.] 



CHAPTER IV 

Thermodynamics 

Internal Energy — Joule's Law of Thermodynamics — Effect 
of increasing specific heat form of adiabatic measure- 
MENT of Cylinder Temperature — Gas Standard of Effi- 
ciency — Flow of Heat through Metal Walls of Cylinder 
— Heat Paths. 

55. Internal Energy. — The applications of thermodynamics 
to the study of gas engine problems are numerous and varied. 
The earlier chapter on the efficiency of cycles of operation will 
have afforded illustration of this, but it is proposed now to 
devote further attention to the matter. 

The relations between P, V and T of unit weight of a perfect 

PV 

gas have been given as — =R ; and in thermodynamic 

calculations it is generally necessary to assume that all gases 
follow this law, which it happens fortunately they very nearly 
do. Specific heat has been defined, and it has been shown 
that the R of the equation above is J (C^ — CJ. 

We now return to the consideration of the- internal energy 
of a gas, referred to in par. 24. The internal energy of a gas 
means the total energy, in ft.-lb., actually in the substance at 
any instant ; to define it absolutely, it is necessary to fix upon 
a definite state of the gas as the zero state, from which to 
measure (usually 100° C. is selected as the starting point). 
Generally, however, we are only concerned with changes in 
the internal energy. If we denote the internal energy by E, 
we know that an increase AE, due to the reception of AH 
heat units while AW ft.-lb. of mechanical work has been done 
by the gas, is given by 

AE= J . AH— AW. 

06 



(HAP. i\ | THERMODYNAMICS 67 

56. Joule s law of thermodynamics is that in a perfect gas 
E depends upon the temperature only : or as it may be more 
generally stated, E is always the same when the gas returns 
to the same state. 

From Joule's law it follows that — unit weight of gas being 
taken — 

AE=JC P . AT 
so that 

JC r . AT=AE=J. AH— AW=J. AH— P . AV 

(an equation which was established in par. 29). 



Thu> 



jAH= JC , AT +P 

AV v AV^ 




or in the limiting case 

J- H = JC — +P (1) 

dV v dV^ K ] 

JTT 

The differential coefficient — , which it is important to 

dV 

note is of the dimensions of a pressure, is an important quantity 
in gas engine expansion and compression curves, and it is 
necessary to find an expression for it which can be more quickly 
dealt with than the above equation (1). 

PV 

Since — =R 

T 

t _pv 

R 

dV R\ "*" dVJ 
R=J(<V- CJ = J C,(y-1), since ^=y 



V 



Therefore — = 1 . ( P+V ~) 

dV JC p (y-l) \ T dV J 



68 THE INTERNAL COMBUSTION ENGINE [chap, rv 
Combining this with equation (1) 



T dR 1 
dV 



P+V — )+P 

y— \\ T* dV ' 



y 



H^w) 



(2) 



This equation is often quoted with the J on the left hand 
side omitted, the H then is supposed to be given in energy units 
(ft.-lb.). 

57. The following table, part of which was calculated from 
an old low compression gas engine indicator card for Professor 
Perry's book on the Steam Engine, affords an illustration of 
the use of the formula (2) — y being there taken as 1-385. 



Compres- 
sion 



Explosion 

and 
Expansion 



V 



25 

20 
14 
10 

10 

10-2 

10-4 

10-6 

10-8 

110 

120 

13 

15 

17 

19 

21 

23 



14-7 
19-5 
29-7 
45-2 



45 

79' 
123 
157 
181 

188 
166 
146 
116 

95 

80' 
68' 
58- 



AP 

aV 



Average 
V 



Average 
P 



-0-96 
-1-70 

-3-88 



173 
218 
173 

120 
33 

-22 
-20 
-14-8 
-10-5 

-7-5 
-6-0 
-5-0 



22-5 

17 

12 



101 

10-3 

10-5 

10-7 

10-9 

11-5 

12-5 

14 

16 

18 

20 

22 



171 
24-6 
37-5 



62-4 
101-5 
140-4 
169-7 
184-9 
177-2 
156- 
131 
106- 

88- 

74- 

63- 



dV 



5-4 
13-4 
140 



4,760 

6,210 

5,230 

3,930 

1,590 
-19-7 
-87-4 
-64-9 
-54-3 
-33-2 
-42-8 
-56-6 



These figures are plotted to scale in Fig. 22. It will be noted 
from the table that during compression is positive in 

every case, showing that dH and dV must be of the same sign. 
As V is decreasing during compression dV must be negative 



CHAP. IV] 



THERMODYNAMICS 



69 



and therefore dH also. So that during compression the gas 
is losing heat to the colder walls of the cylinder. The ratio of 
loss is not great, however, and such as it is it represents the 
differential effect of the cooling of the walls and the heating 
by contact with and radiation from the hot piston. During 
explosion the gas is seen, both from the table and the curve, 



6.000. 



spoo. 



3.000. 



2000. 



UOOO. 



Curve showing%Q 
during Explosion 
and Expansion. 



dV 






Zero Line 




1 








■moo 


V 


( 


\ 


10 




if 


k 


2$ 



dH 

Fig. 22. — Curve of and V. It shows how the working stuff receives 

dV 
heat during explosive combustion and how it afterwards loses heat to 

dfT 
the walls. Unit of V is arbitrary so unit of — — is arbitrary also. 



to gain heat rapidly until the point of greatest pressure and 
temperature is reached, and then the curve falls rapidly, and 
the gas begins to show a loss of heat to the cooling walls. This 
loss has of course been going on during the explosion also, but 
the effect is masked by the far greater quantities of heat then 
being liberated. In modern engines, pressures and tempera- 
tures are higher, so that increase of specific heat affects the 



70 THE INTERNAL COMBUSTION ENGINE [chap, iv 

calculation and must not be neglected. This correction is 
dealt with later on in the chapter. 

58. It is often found that during compression or expansion 
the eras will follow the law 



so that 



P V n = constant— c, say 
c?P_ nc 

= _ n -pyn x J _n¥ 
Y«+i y 

or V— =— nP. 

dV 

Substitute this in equation (2) 

and J *l=J_|^p + yp]=y=^p ... (3) 

dV y—\ { ^ Y ) y—\ K \ 

A very simple expression which can often be used to obtain 
results speedily. If the gas lose in H during compression 
evidently (y — n) must be positive or y must be greater than 
n. During expansion, if the gas is losing heat (y — n) must 
be negative or n be greater than y. (Cf. Ex. 14 on p. 40.) 

This analysis was originally due to Professors Ayrton and 
Perry, and published by them in the Proceedings of the Physical 
Society in 1885. 

59. Effect of Increasing Specific Heat. — It is important to 
examine how this calculation is affected when allowance is 
made for a specific heat which increases with temperature. 
It was mentioned at the close of last chapter that the gaseous 
mixtures used in practice had a specific heat value rising in a 
linear relationship with temperature — in fact that 

C = /9+iT 

where ft and s were some constants. 

Since (C„ — CJ must from Joule's law be independent of 
temperature, it follows that 

C p =a+sT 



chap, iv] THERMODYNAMICS 71 

where s has the same value as above, and a is a new constant. 

The ratio may for convenience be written c ; it is obviously 

P 
the value of y when T=0. 

It has just been shown (p. 67) that for unit weight of gas 

J d - K =JC ^ T +P 
dV v dV 

Also that d *=±(*+V d £\ 
dV R v dV' 



therefore 



so that 



but R=J(C^— C p )=J(a— 0) 

dV J (a— p) V dV' 

jdK = l+W ( p+v dPN +p 



i ^ a— /J J ^ rfV a— 



sT 



If dP dV 

1 aP+6-TP+ 0V— +*T\r' 



so 



a—p{ ' ' dV ' dV, 

that J^^^fcP+V^U-^-lp+V^l ... (4) 



and this is the new r expression for — . 

If s = ; i.e. if specific heats were constant, equation (4) 
w T ould clearly at once become equation (2). 

As before, take the case where, as in compression and expan- 
sion, PV" = constant, very nearly. 
Then 

V— =-nP, 

dV 



72 THE INTERNAL COMBUSTION EXGIXE [chap, iv 
and substituting in equation (4) 

d\ c—l a—p I 



or 



r/V I c—l ft— g I 



(5) 



which becomes equal to equation (3) if s = 0. 

Equation (5) shows that — is proportional to P when T 

is constant, and that it is a linear function of T when P is 
constant : provided always that all changes are regulated 
by the law PV" = constant. 



CRANK ANGLE EXPANSION SIDE 



Ah 






<3 

cs 




NO 

CS 




CM 




o 


O 


CRANK 


ANGLE 


COMPRESSION 


SIDE 







Fig. 23. — Indicator diagram analvsed in Fig. 23a. (It is Fig. 5 of the 7th 

Report of G.E.C.) 



Mr. Hogg has applied this method of analysis to an indica- 
tor diagram taken with a reflecting indicator by Prof. Dalby 
and reproduced in Fig. 23. The following are his results. 

Value of n dining compression 1-372 ; during expansion 
1-435. Composition of gas sensibly the same as that adopted 
as standard by G.E.C. whose specific heat figures are therefore 



(HAP. IV 



THERMODYNAMICS 



taken. Correction for chemical contraction on explosion 2-24 
per cent. 





Compression 






Expansion 










JrfH 








JdH 




P (abso- 




dV 




P (abso- 




dV 


Crank 


lute) 


6° C 


ft. -lb. per 


Crank 


lute) 


e° C 


ft-. lb. per 


Angle 


lb. per 




cub. ft. 


Angle 


lb. per 




cub. ft. 




sq. inch 




per lb. of 
gas 

l 




sq. inch 




per lb. of 
gas 


350° 


139-8 


474 


-1610 


370° 


317-5 


1,462 


-32,600 


340° 


102-5 


327-6 


-333 


380° 


281 


1,405 


-27,800 


330° 


84-0 


292 


-105 


390° 


230 


1,308 


-21,300 


320° 


67-4 


252-7 


-57-2 


400° 


184 


1,194 


-15,670 


310° 


54-3 


221 


+ 149 


410° 


152 


1,142 


-12,420 


300° 


430 


183 


+ 211 


420° 


119 


1,017 


-8,750 


290° 


36-2 


169-5 


+ 204 


430° 


96-0 


926 


-6,490 


280° 


30-3 


149 


+ 205 


440° 


80-5 


872 


-5,150 


270° 


260 


132 


+ 201 


450° 


68-3 


816 


-4,120 


260° 


— 


— ■ 


— ■ 


460° 


59-6 


781 


-3,450 


250° 


— ■ 


— 


— 


470° 


51-8 


732-5 


-2,840 


240° 


— 


— 


- I 


480° 


47-9 


729-4 


-2,620 


230° 


— 


— 


— ■ 


490° 


430 


686 


-2,230 


220° 


— 


— 


— 


500° 


401 


667-8 


-2,030 


210° 


— 


— ■ 


— 


510° 


37-7 


646-9 


-1,855 


200° 


14-3 


77 


+ 154- 5 


520° 


34-2 


582-9 


-1,540 


195° 


■ — 


— ■ 


— ■ 


530° 




— ■ 


— 



These figures are plotted in Fig. 23a, and they show the gas 
to be just losing heat on balance from A to B on the com- 
pression stroke, and to be gaining it from B to C. Ignition 
occurs about the point C, and the curve would then shoot up 
far off the diagram ; this rapid rise cannot be got from the 
indicator diagram as the volume alters so exceedingly 
slowly at the dead centre. From this height, however, the 
curve rapidly descends owing to radiation and convection 
losses until the point D is reached. The rate of cooling then 
tends to decrease as shown by the line DE, which represents 
the expansion period. The gas is still losing heat at the point 
E, when the exhaust opens and the temperature is in the 
neighbourhood of 600° C. 

Mr. Hogg's curve shows no evidence of any continuation 
of combustion after the highest temperature has been reached. 



74 THE INTERNAL COMBUSTION ENGINE [chap, iv 



IQOQO 



lOfiOO __ 




20,000 _ 



3qaoo — 



Fig. 23a. Change of Internal Energy during compression and expansion 
strokes of diagram shown in Fig. 23. 



60. Adiabatic law with variable Specific Heats. — If 



dH. 

dV 



be 



zero, or, in other words, if the transformation be adiabatic, it 
follows from equation (4) that 

dV dV 

r/P+6-TP+ pV- +*TV --=0 
d\ dV 



or 



V 



dV a+sT 
dN + p+s^ 



P=0. 



(HAP. 1V| 



THERMODYNAMICS 



75 



If 



i) this would become 



V>P=o 

d\ 

which integrates as in par. 29 to the familiar form PV V = 
constant. If, however, s is not zero we have a much harder 
integration. The above equation becomes 

dV 



dP a+sT 
P~ )i+sT 



P\ 



Also since = constant 



T 



V 



PV 



=0 



(1) 



P V 

T T T 2 



dV t dP 

or ^7+^7- 



dT 
V ' P Y 

Equation (1) may be written 
R dP. dV 



(I 



(2) 



dP dV 

P^~~V 



=0 



or using (2) 



Q dP dV ^ 



= 



The integral of which is 

/?logP -(- alogV-f- 6-T = constant 
and this may also be written 

P^. V a . e sT = constant. 
This is therefore the adiabatic law with variable specific heats. 
61. Expariments on Measuring Temperatures during the 
Cycle of Operations in a Gas Engine. — Professor Burstall * 
was the first to do this. He came to the conclusion that 
with a platinum thermometer it was impossible, owing to 
the fusing of the fine platinum wire before a sufficient number 
of observations had been taken, to make such measurements 
with an engine working on full load. He had therefore to 
experiment on an engine running light and firing but once in 
each twelve revolutions. The principle upon which a plat- 

* Phil. Mag., 1895, and Proc. I.M.E., 1901. 



76 THE INTERNAL COMBUSTION ENGINE [chap, iv 



inum thermometer works is that since the electrical resistance 
increases with the temperature in accordance with a known 
law, to measure the resistance of the wire is to measure its 
temperature at the moment. Professors Callendar and 
Dalby * have since made additional tests in this direction. 
These experimenters realized that they could not get a wire 
which would " stand up " to the temperature of explosion 
unless it was so thick that it must fail to follow the fluctuating 
temperatures of the gas with sufficient rapidity. They there- 
fore decided so to arrange the apparatus that they could with- 
draw the fine thermometric wire from the action of the gases 

C 




Fig. 24. — Combined Admission and Thermometer Valve (Callendar). 

during explosion, and replace it for each suction and com- 
pression stroke. This was effected by fitting up the inlet 
valve as shown in Fig. 24. C is the admission valve casting, 
which is bolted on to the cylinder and projects inside the space 
provided for it. The thermometer was inserted through the 
spindle of the main admission valve marked A, which had been 
drilled out to receive it. In the figure the little " thermometer 
valve," as it may be called, is shown projecting beyond the 
main valve head into the cylinder. It closes with a little 
conical seating of its own as soon as the ignition point gets 
near. The thermometer leads enter through B, pass along 
the thermometer valve spindle until they arrive at the fine 
platinum wire which is shown at P. The head of the ther- 
* Royal Soc. Proc, 1907. 



CHAP. IV ] 



THERMODYNAMICS 



77 



mometer valve is connected to its spindle by the two ribs 
which are made as thin as possible so that the platinum wire 
is not screened more than can be helped from the action of 
the hot gases when the thermometer valve is pushed out into 
action. The opening and shutting of the thermometer valve 
at the proper times is effected by suitable mechanism. The 
thickness of the platinum wire was Trhrb °^ an mcn - At about 
130 R.P.M. the lag of the thermometer was not more than 10° 
of crank angle with a temperature fluctuation of nearly 200° 
in half a revolution. This would correspond to a time lag of 
^Xt%= 0-013 sec, which was quite good enough for 
measuring anything so relatively steady as the suction tem- 
perature. As a result of such measurements it was found that 
the suction temperature varied with the conditions of running 
from about 95° C. at light load to about 125° C. at full load, 
the air temperature being about 20° C. and the jacket tem- 
perature 27° C. The following are details of two tests — 



R.P.M 

Ratio air /gas 

Atmospheric temperature 

Jacket temperature 

Temperature of thermometer valve at 

360° crank angle 

Ditto at 26° crank angle 

Corresponding pressure at ditto . 
Molecular contraction on combustion 



Test I. 



130 

71 

20° C. 

27° C. 

122° C. 
111° C. 

18-5 lb. /in. 2 
4' 3 per csnt. 



Test II. 



114 

5-8 
21° C. 

27° C. 



130° C. 
17-8 lb. /in. 2 
5-1 per cent. 



It was noted that by a curious coincidence the indicator 
cards from these two trials showed a practically identical 
expansion curve, not varying by more than 1 lb. /in. 2 at any 
point. The temperatures during expansion were however far 
greater when using the richer mixture, and the heat losses to 
the walls correspondingly greater, so that although much 
more gas is used in one case than in the other, no more H.P. 
is obtained, the excess heat units going to waste. 

These experiments show that the convenient practice of 
assuming the suction temperature to be 100° C. irrespective 



n THE INTERNAL COMBV-i: )3S ENGINE [chap, iv 

of load is only approximately correct. When, as in the 

experiments, the suction pressure is accurately measured, it 
is possible to calculate accurately the temperatures throughout 

"-: "" .- hen _ he:: gas law and a knowledge of the 

molecular contraction on combustion. 

Li'f: Ert-e: r — _ :-.te: :-.Ttempt5 to measure the 

temperature of the gas are doe to Coker and S coble. They 

::.__". "It i _ .::t::r. TtIi:^:':-.:^^ :: i-e^r hrm •; : : ^ :; ihXr 
:.: there Hi t ha~e orri -pedal circumstances causing the 
. .._---■ t ■■"-.■".-: - . n~iihl : their chief work. however is 
v.t iiee.-eireiLezi: :: teiepe: .-i".:e Ei_:r.; t:ie ez:: .-,r_-:: :: i-irve 
iie~e -..:.- ...i:_:_ Hire :ei::n measurement use was 
ii : - - - - - made np of alloys of platinum with 

rhodium and iridium, which have very high fu sin g points, rolled 
:r -~:v" - : :• : ~t " t ■ : v : r . - - : . . ' - - : :. iths of an inch thick. In 
~ '.:.!' "".-"" "." ""■-::"""..:"."."'—:"'. e " : ::e-- "".:e the ;::-.« "tHh-htht 
hi: M1I7 the _.-.._ impression curve, hut also along the 
_:-"-: :" : :it -:::: :-n: ::. ::zr^e the very highest tem- 
peratures had still to be estimated, however, by regarding the 

iiat^e itseh ■- n~ "'.-... :ne:e: hiie highest temperature 
v ihite : : "hi he Hire - : e :- ley e~tin;.te . ie_ "hie ~ \-.~ tiieii "'17 
inferring them from the suction temperature, since ( 1 ) it was not 

.1 - : - — - 1 „_ 1 1 : ] _ e:_ 1 : h Dntraction, (2) and the perfect 

gas law is more truly followed at high temperatures. It was 
hi > 1 : hi i -.. ■- - the 1: r hi :ein:: e: 1 "in iii_ the .i^^ii. the iteth::- 
bourhood of ISC' and may with specially rich mixtures 

e~en :et :n _ '•'.■. " . 
ho. G-is Stiiiii:: :: Erhciez:".— n hi: II -he :- 

- ..hi". : efhnee.17 ::: nt-e:eiih : imbustion engines was 
explained rally, and numerical results were given. The stan- 

" ■- : . >■ --"i- hi~e~e: hi " _i 1 : :ve "_■_:- ~ :: e:. ':e ::ne"^i 
e 1- . .1^11.7 e~en ~ere 1 v source of loss removed. The 
1 - - « ; :;. : : 1 7 hi? :- the.: the 11 se i::> iitizttire ezitt. H'ei ::i ::?. leiie. 
vh el 11 i._h " -i 1- 7 11: :i:e>::.s er.ene-7 -: :c: ~nt ::: 
: ; :_«e -i. :- : - > 11. itrreit t : - sstine : - > :.. : :te it. tie : .-._:/.- 
.'-111 h 11 -~ ■".". ■".-: ■". -ih:i-r.:iT- hn.t the ^e:i:: lie?.: > 
constant. 

It is therefore necessary to make allowance for this, and 
one way of dohtu - > to replace the " air standard " with a 






(ii.vr. iv| THERMODYNAMIC'S 7!) 

" gas standard " based on the mixture commonly used in a 
gas engine. The best mixture to use is that for which the 
Gaseous Explosions Committee determined the specific heat- 
temperature relationship. 

As stated on p. 63, this curve corresponds to a linear law 
between specific heat and temperature agreeing with the 
observed results within the limits of experimental error, as 
follows : 

C v = 0-152 +0-000075 T, 

where T is the temp, absolute. This mixture is stated in the 
Report to be "the mixture on which Clerk experimented." 
Reference to Clerk's paper (Proc. Royal Society, A., Vol. 77) gives 
the following particulars of this mixture : — 
Extreme compositions — 

Vols. Vols. 



Steam (assumed gaseous) 


. 11 '2 and 12*7 


Carbonic anhydride 


4-8 „ 5-5 


Oxygen. .... 


8-7 „ 7-0 


Nitrogen .... 


. 75-3 ,, 74-8 



1000 1000 

Corresponding respectively to explosive mixtures containing 
before combustion 1 volume of gas to 9-8 volumes of air, and 
1 volume of gas to 8-5 volumes of air. The lower heat value 
of the gas was 574 B.Th.U. (or 319 pound-calories) per standard 
cu. ft., whilst the compression volume was 18-59 per cent, 
of the total volume. Clerk mentions on p. 334 of Vol. I of his 
Gas, Petrol and Oil Engine that a standard cubic foot of this 
mixture weighs 0-07833 lb. So that if the specific heat be 
expressed as ft. -lb. per standard cu. ft. (i.e. as volumetric heat) 
it becomes 

== 16-6+0-0082 T. 

With this data it is possible to calculate the temperature at 
any point in the ideal constant volume cycle (see Fig. 7, the 
lettering of which is also followed in what follows), provided 
that the suction temperature be known. This may conveni- 



BO THE INTERNAL COMBUSTION ENGINE [chap, iv 

ently be taken as 100 c C. . a figure never far from its actual 
value, and one moreover which agrees with the use of that 
temperature as a starting point for internal energy nieasure- 
ments. We may assume for simplicity's sake that our ideal 
engine cylinder when filled at the end of the suction stroke 
contains exactly one standard cu. ft. of gaseous mixture made 
up of a small proportion of exhaust products together 
with fresh air and fresh gas. The anioimt of the exhaust pro- 
ducts will vary with the compression ratio, but no great error 
will be made by taking it that at the end of the suction stroke 
the contents of the cylinder (at 100" C. ) are such as to have an 
average calorific value of 29 pound calories, being made up of. 
say. 1 part by volume of gas to 10 parts by volume of a com- 
bination of air and exhaust products, so that the volume of 
gas present is one-eleventh part of a standard cubic foot 'con- 
taming 319 -j- 11 or 29 pound calories of heat energy. 

64. The Adiabatic Curves of Compression and Expansion 
(var. sp. heats). — The theoretical efficiency of the new standard 
cycle can now be worked out for various compression ratios, 
assuming no heat loss, no chemical change of volume, no change 
on explosion of the relationship between specific heat and 
temperature, no combustion after the point of maximum 
temperature, and the suction tempera tine constant at 100" C. 
Knowing the suction temperature (To), the temperature at the 
end of compression (TJ can be calculated from the adiabatic 
formula appropriate to a linear relationship between specific 
heat and temperature. Having the compression temperature 
(Tj) it is easy to obtain the explosion temperature (T 2 ) from 
the heat liberated (29 pound calories), and the known specific 
heat values. The temperature at the end of expansion (T 3 ) 
is obtained from the same law as that governing compression. 
All four temperatures being then known, and the internal 
energy corresponding to each, the calculation of efficiency 
follows at once. 

The adiabatic law corresponding to a linear relationship 
between specific heat and temperature is as given in par. 
p p y« g.T = constant. 

PV 

But — = const ant. 

T 






THERMODYNAMICS 



CHAP. IV ] 

Therefore Y*+. e sT . T 3 =constant. 

» o \ / J- o 



81 



Or 



m © 



,*(To-Ti)_.j 



> \ -r X l V e *(Ti— To) 




aar-m 



(Ti-To) 



V,/ VT , 

V_o\ /TV 
Vy VT , 

It is not possible to calculate T r directly from this, but 
curves may be drawn giving the relationship of temperature 
and compression ratio, and in this way T x for any given volume 
ratio (r) may be found. 

Now T =373, and C= {3+sT = 0-1 52 +0-000075 T. 

To get C p we need R. 



Now C, 



C p -C=0-071 



R _ PV _ 147X144 

C v = j and R= r r r- . 078 33 X273 - 



99 ; and 



So that C J =a+6-T=0 : 223+0-000075 T. 
Therefore 

'V«\ n ,. ! /Ta , T x — 373 



log, (£)=*14 log, (*i) 



950 



log e r. 



The relationship of T x and r are shown in the Table below. 



*1 


T, 


r 


(continued) 


T 1 

(continued) 


r 

(continued) 


100 


373 


1 


1,100 


1,373 


46-5 


150 


423 


1-38 


1,200 


1,473 


60-1 


200 


473 


1-85 


1,300 


1,573 


771 


250 


523 


2-39 


1,400 


1,673 


973 


300 


573 


309 


1,500 


1,773 


122 


350 


623 


3-89 


1,600 


1,873 


153 


400 


673 


4-86 


1,700 


1,973 


190 


450 


723 


5-97 


1,800 


2,073 


235 


500 


773 


7-24 


1,900 


2,173 


289 


600 


873 


10-4 


2,000 


2,273 


353 


700 


973 


14-7 


2,100 


2,373 


430 


800 


1,073 


201 


2,200 


2,473 


522 


900 


1,173 


26-9 


2,300 


2,573 


631 


1,000 


1,273 


35-6 









G 



H THE INTERNAL COMBUSTION ENGINE [chap, iv 



By plotting the values of T 2 and r from this Table, it is 
possible to deduce the values of T a for specific values of the 
compression ratio, as shown below. 



Corresponding Yaxttes <ot r and Temp, 
i or Compression. 



AB: 



A3 ZND 



r 


r, 


- 


r« 


1 


373 


9 


831 


2 


487 


10 


861 


3 


567 


11 


**7 


4 


629 


12 


-U 


5 


680 


13 


937 


6 


725 


14 


- >li 


_ 


763 


15 


-; 


8 


799 







.-' .- .-> 



POC 



< 



J 6 







---.- 



M 



TIT 



Z= 



^— <- 







— 



SS 



_ 



z: 



S 



Voi-UME //• CUBIC FEET 

Fig. 24a. — Compression curves for one cubic foot of air original^ :-.: 

CB with constant specific beat (PV ^ = eonst : ! A with variable 
specific beat (gas engine mixture). 



CHAP. L\'J 



THERMODYNAMICS 



83 



It is useful to express these temperatures in other than 
the absolute form, and to compare them with the corre- 
sponding temperatures obtained from the adiabatic law for 
a perfect gas with constant specific heat, viz. PV 1,41 =con- 
stant. This comparison is given below, and is illustrated in 
Fig. 24a. 





6°C. 


6°C. 




r 


(var. specific 


(const, specific 






heat) 


heat) 




1 


100 


100 




2 


214 


223 




3 


294 


312 




4 


356 


386 




5 


407 


449 




6 


452 


505 




7 


490 


555 




8 


526 


602 




9 


558 


645 




10 


588 


686 




11 


614 


724 




12 


641 


760 




13 


664 


795 




14 


686 


828 




15 


708 


859 





65. Internal Energy Throughout Cycle. — Having thus found 
T! for various values of r, it is next necessary to obtain T 2 the 
explosion temperature, and this is best got from an internal 
energy curve. 

Volumetric heat = 16-6 +0-0082 T 
and the internal energy 

r t 



373 



(16-6+0-0082 T)dT 



= \CrQ (T— 373) + 0-0041(T 2 — 373 2 ) ft.-lb. 
This is shown plotted in Fig. 25. Now on explosion, 29 



84 THE INTERNAL COMBUSTION ENGINE [chap, iv 



























6o,(. 


inn - — — 










































: 2 






r 






: z 


5o,< 






}{j\j ~ 


z. 






v 






t 






: 2 












2 ! 






1 






T 






7 


40/ 




, 


U(J j 


7_ , 






* 












'- 1 ~ 






_ j. 






__/ 






.7. 














£5 3°t 






00 — r~~ 




c 






<i> 






c; 






"^ 








•td z 




1) 


J- - 




c: 


V? V 




* 


X 7 




t 2O,0 


~m / 




OO ~ — ~ /~ ~ 














• 




«$ 7 






s> /- 












v. / 






* Z 






**» Z 




top 












*> -v 






"ft -7 












5 Z 






Z 






<^ z 






*** Z 






18 z 






»< __^_ 






O 500 ° /,0(?J° 


/,soo° 2,000 ° 2,SOO° 






Temperature Cervtx.gra.de 

Fig. 25. — Internal Energy — Temperature graph for Gas Engine Mixture 

(G.E.C.). 



pound-calories of energy are given to the gas, equal to 29 X 
1400 = 40,600 ft. -lb. The values of the energy for various 
values of the temperature can conveniently be plotted from 
the above equation, and if to the energy value at any particular 
compression temperature 40,600 ft. -lb. be added, the total is 
the energy figure for the corresponding explosion temperature. 
Then from the same energy curve the explosion temperatures 
can be themselves deduced. These temperatures can be sub- 
quently checked by calculation where necessary. The follow- 
ing are the results obtained : — 



CHAP. IV] 



THERMODYNAMICS 

Table of Temperatures. 



85 





0o°C. 


e^C. 


2 °C. 


«,°c. 


r 


(suction) 


(compression) 


(explosion) 


(exhaust) 


1 


100 


100 


1,660 


1,660 


2 


100 


214 


1,730 


1,415 


3 


100 


294 


1,780 


1,290 


4 


100 


356 


1,820 


1,205 


5 


100 


407 


1,850 


1,145 


6 


100 


452 


1,880 


1,100 


7 


100 


490 


1,905 


1,060 


8 


100 


526 


1,930 


1,025 


9 


100 


558 


1,950 


1,000 


10 


100 


588 


1,970 


976 


11 


100 


614 


1,990 


955 


12 


100 


641 


2,010 


936 


13 


100 


664 


2,025 


920 


14 


100 


686 


2,040 


904 


15 


100 


708 


2,050 


889 







Table 


of Energy and Efficiency 








Internal Energy in Ft. -lb. 




Thermal Efficiency. 


r 


E 
(Suc- 


(Compres- 


E 2 

(Explo- 


E 3 

(Exhaust). 


"Gas 
Stan- 


" Air 
Stan- 


Ratio of 
Gas Stan- 
dard to 




tion). 


sion). 


sion). 




dard.'' 


dard." 


Air. 


1 








40,600 


40,600 










2 





2,300 


42,900 


33,000 


0-188 


0-242 


•78 


3 





3,950 


44,550 


29,200 


0-281 


0-356 


•79 


4 





5,300 


45,900 


26,7£0 


0-341 


0-426 


•80 


5 





6,450 


47,050 


25,000 


0-384 


0-475 


•81 


6 





7,450 


48,050 


23,700 


0-417 


0-512 


•81 


7 





8,300 


48,900 


22,600 


0-443 


0-541 


•82 


8 





9,100 


49,700 


21,650 


0-467 


0-565 


•83 


9 





9,900 


50,500 


21,000 


0-483 


0-585 


•83 


10 





10,550 


51,150 


20,350 


0-498 


0-602 


•83 


11 





11,200 


51,800 


19,800 


0-512 


0-617 


•83 


12 





11,850 


52,450 


19,300 


0-524 


0-630 


•83 


13 





12,400 


53,000 


18,850 


0-536 


0-642 


•83 


14 





12,950 


53,550 


18,450 


0-545 


0-652 


•84 


15 





13,350 


53,950 


18,050 


0-555 


0-661 


•84 



B6 THE INTERNAL COMBUSTION ENGINE [chap, iv 

66. Gas Standard. — It is now possible to give the value 
of the internal energy at each of the four corners of the diagram, 
and so to obtain the thermal efficiency corresponding to each 
compression ratio, as shown on p. 86. 

It will be seen that with this gas mixture the gas standard 
is about 80 per cent, of the air standard for the compression 
ratios in common use.* It corresponds very closely to the value 

■ - (T 

67. Approximate Formula for Gas Standard. — It is not diffi- 
cult to show that to a first approximation the " gas standard " 
efficiency is given by the expression 



^l 1 — I 1 " n) n 



c-1 



where rj=\ — ( — ) 

Or if it be preferred, the following approximation may be used 

It is a useful exercise for students to compare this approximate 
rule with the figures of p. 85. 

68. Hopkinson's Efficiency Experiments. — In a paper pre- 
sented to the Institution of Mechanical Engineers in 1908, 
Prof. Hopkinson described certain experiments he had made 
to determine the relationship of actual engine efficiency 
with the " air standard " and with what we have termed the 
" gas standard." His results are conveniently summarized 
in Fig. 26. The uppermost dotted curve is the " Air Stan- 
dard " which for the compression selected (viz. r = 6-37) 
comes out at 52-2 per cent. Under that is a line which was 
calculated by Hopkinson on the basis of a variable specific 
heat (using the figures of Holborn and Austin, and Langen). 
Below that again is the line of efficiencies as actually found. 

* Prof. Asakawa (Brit. Association, 1913) has studied experi- 
mentally the effect of variation of compression ratio on thermal 
efficiency. It appears that about 85 per cent, of the "gas standard " 
efficiency may be expected as "indicated thermal efficiency " in practice. 



. 



HAP. IV] 



THERMODYNAMICS 



87 



60- 



40 



20 



The second line was calculated by an approximate graphical 
method. 

69. Choice of Working Fluid.— What change would be 
effected in the thermal efficiency of an engine if the working fluid 
were changed for one having a larger specific heat ? This is 
an important problem, as it not only concerns the choice of 
working fluid, but also whether it is well to work high up the 
temperature scale or not (the specific heat increasing with the 
temperature as has been shown). 

The thermal efficiency of an engine depends on many factors, 
but to a first approximation it may be taken as proportional, 

"Air Standard" Efficiency (52-2 %). 



s> Hop kin son 's Curve of Ideal 

limiting Efficiencies . 



& 

QJ 




Actual thermal Efficiencies 
as measured by Hopkinson ., 



Percentage of Coal gas in Cylinder Contents 



4 



10 



12 



Fig. 26.« — Hopkinson's measurements of actual thermal efficiency for mix- 
tures containing from 8 to 12 per cent, of coal gas, compared with his 
calculated ideal limiting efficiency curve. 

for any given compression, to the efficiency as obtained from 
the " Air Standard " formula 

R 



Now 
so that 



J(C„— C t )=R and y— 1= 



JC. 



log (1— Tj) 



1 \J* 



_R_ 
JC. 



R 1 l 

"tp log — 



88 THE INTERNAL COMBUSTION ENGINE [chap, iv 

differentiate JL = log r. 

1 — t]dC v JC V 2 

chj R(l— rj) 

= — — log r. 

dC v JC,* 6 

Therefore with increase of specific heat the efficiency jails. 
This could also be written 






This gives the proportional change in efficiency for a given 
proportional change in specific heat. 

If for example y = 1-40 and r = 10, then for a 1 per cent, 
increase in C v the corresponding proportional decrease in 
efficiency would be 

— j(l-4— 1)— ? log e lo| 

ioo r } n 6e j 

Now when r = 10, r\ = 0-60 

and _J=]0-40 X X2-30 X — 

r\ \ 0-60 * 100 

= 0-61 per cent. 

So that in this case the efficiency falls by rather more than 
J per cent, when the specific heat rises by 1 per cent. 

70. Heat Flow through Cylinder Walls. — One of the most 
important matters connected with the temperature changes 
in an internal combustion engine is the consideration of the 
manner in which the heat carried away by the cooling water 
passes from the hot gas to the water. The cooling water is 
circulated around outside of the cylinder in a space provided 
between the cylinder walls and the jacket. The carrying away 
of heat by this cooling water is, of course, of no thermal advan- 
tage to the engine, much the contrary, in fact ; but unless it is 
allowed to take place the cylinder walls would reach so high 






(hap. iv] THERMODYNAMICS 89 

a temperature that lubrication would become impossible. 
Engines become more efficient as this heat loss is reduced, 
but care has to be taken to limit the reduction at the point 
where there would be risk of the lubrication failing. If the 
lubrication did so fail the piston would seize and the engine 
be seriously damaged. In a four-stroke engine of the usual 
type the temperature of the gases inside the cylinder will vary 
during the cycle from about 20° C. to 1500° C. This is a large 
range, but it is found that the wall temperature — even that of 
its innermost face — does not pass through anything approach- 
ing so large an amount. With a temperature range in the gas 
of the amount mentioned the total temperature range in the 
inner face of the wall will not exceed about 10° C. And even 
this small range is but skin-deep. It has been shown mathe- 
matically, and confirmed by experiment, that at a depth below 
the inner surface of the wall of ^g inch the temperature range 
is only about ^5-oth part of the range at the surface. The 
following comparative statement can therefore be given as an 
illustration : — 

Range of temperature in gas — about 1500° C. 

,, ,, ,, in wall surface— about 10° C. 

,, ,, ,, yg- inch deep in wall — about ^V° C. 

For all practical purposes, therefore, the wall temperature 
as a whole does not vary from moment to moment during the 
cycle. 

The temperature is different, however, in different parts of 
the length of the wall. Thus, the wall is hotter near the com- 
pression head than it is at the other end of the cylinder. This 
is because most of the heat loss occurs at the beginning of the 
stroke, in the clearance space, where the highest gas tem- 
peratures are found. The consequent varying amount of 
expansion in the different cylinder parts renders the metal 
liable to crack unless the design provides room for expansion. 
Cylinder heads and pistons are the most difficult parts to pro- 
tect against cracking, particularly in large engines. But if 
fixed joints between metal faces necessarily at different tem- 
peratures are replaced by sliding ones, much of the trouble 
may be removed. 



THE INTERNAL OOllBtJS'tlON ENGINE [chap, it 

71. Hopkinson's and Coker s Experiments on Cylinder Tem- 
peratnres. — Experinients made by Hopkinson * and by Coker f 
on different engines afford a basis for drawing up a table of 
the probable temperatures occurring in the ordinary type of 
fonr-stroke engine (open ended) : — 





Temperature. 


1,900° C. 


400 : C. 


. : : 




250 : 




250 . 




200 ; 




loo* : : 




_ : : C. 




65^C. 



Part. 



'. ' -nrrm-m temperature of gas. say, 

I isi mi rZ-tre of face 

-..-:- :: ?xhausl vahne 

Z'lTT'i inlet valve 

TTnjacketed part of wall in clearance space 

I rton, edge of face 

Jacketed wall in. clearance space . 
~\ ■:'_-:-: r :: : _ :_ wall in stroke 

: I'ling water at outlet 



Coker also found that with a copious supply of cooling water 
there was no difference in wall temperature along the length 
of the stroke. But with a restricted supply the average wall 
temperature was less (by some 7 : C.) in the metal near the end 
of the outward stroke than at the beginning. Thus when the 
cooling water is restricted in quantity some of the heat passing 
into the cylinder walls travels along the wall as well as through 
it. 

An interesting measurement made by Hopkinson showed 
that if any part inside the cylinder should rise to 700 ~ C. the 
gases would ignite spontaneously, so causing pre- ignition. 

72. Mathematical Theory of Wall Temperatures. — It is 
interesting to investigate this problem mathematically. 

Let 00 be the inner face of the section of the wall which can 
with sufficient accuracy for this problem be considered plane. 

:._-::1t. what is happening at A, distant x below the surface 
of the metal. Across an imaginary unit area perpendicular 
- the surface of the paper and to the line of flow of the heat 
which is in the direction of the arrow, heat will be transmitted 

* Proc. I.C.E. 1909. 

t Proc. I.C.E. 1913. 



CHAP. IV] 



THERMODYNAMICS 



01 



but a part will be retained for the heating up of the substance 

of the lamina at A. At a section at distance (x -f- fix) the 
temperature will he (6 -\- $0), where of course $0 is negative, 



1 



Heat flow to 

^ Cooling water. 



X 



Fig. 27. 



at the same moment of time. Now the rate at which heat is 
received at the left face of the lamina, contained by the two 

planes at x and (x ~\- dx), is equal to — k — where k is the 

dx 

conductivity, and the additional amount which flows out per 



7 d2 Q * 






second on the other side is — ( — k — ) dx = 

dx \ dx/ 

Now this heat must be equal to that required to raise the tem- 
perature of the lamina between the time t and the time (t -{- 
St), and the volume of the lamina being (1 X 1 X dx) — dx, it 

follows that the heat so absorbed must be equal to 6x w 



dt <r, where w 
heat. 



weight of unit volume and a- 



dt 
specific 



92 THE INTERNAL COMBUSTION ENGINE [chap, iv 
Therefore 

— k — ^ bx bt = — wcr — bx bt 
dx 1 dt 

k d 2 d dd 
or — — _ (1) 

wcr dx 1 dt 

This is the equation for the flow of heat. The same equation 
occurs in problems relating to electric conductivity, to the 
diffusion of liquids into each other and to many other phy- 
sical applications. Its solution is therefore well known, and 
in this case the simplest form of it is 

Q=Ce- ax sin(yt— Px) (2) 

where C, a, y and p are constants some of which can imme- 
diately be determined from equation (1). 
From (2) 

rlf) 

=yCe~ aX COS(yt — px) 

dt 

d ^=—aCe- ax sin(yt—px)—pCe- aX cos(yt—px) 
dx 

d 2 6 

—=a 2 Ce- aX sm{yt—px)-i r apCe-- 0X cos(yt—px)-±apCe~ a *cos 
dx 1 

{yt—px)—p 2 Ce- aX sin(yt-Px). 

= (a*—p 2 )Ce- ax siYi(yt—Px)+2apCe- ax cos(yt—px) 

So that equation (1) may be written 

—l(cP—p)Ce-**.m (yt-px) + 2apCe- aX cos (yt—px)\ 
wcr ( ) 

= yCe~ ax cos(y/ — Px). 
For this to be an identity 

a 2 — p 2 =0 

k 

and Zap — =y 

wcr 

Now since when x = a, the value of 6 may be regarded as 
the zero from which the temperature is measured, it follows 
that a must be positive and real. 






chap, rv | THERMODYNAMICS 93 



So that «=^V ~ 

Substituting in equation (2) 



(3) 



73. Skin Temperature. — Now when x = o the value of 
6 is that for what may be called the skin temperature of 
the metal — call this o 

therefore = Csinyt, 

This calculation indicates the existence of a skin tem- 
perature in the metal which rises and falls as a simple 
harmonic function of the time with an amplitude of C, 
that is to say the range of temperature in the skin is 2C. 
Now imagine the wall to be in contact with a highly heated 
gas the temperature of which fluctuates rapidly and unevenly. 
It is well known that by Fourier analysis this temperature can 
be represented by a series of simple harmonic functions of the 
time, of increasing frequencies. In a gas engine the temperature 
of the gas rises and falls about a mean value in what is roughly 
a sine curve, and in any case the addition of two or three upper 
harmonics should make the representation very close. The 
effect of high harmonics at the interior part of the wall is, how- 
ever, slight ; since it will be observed that the logarithmic 
decrement factor in equation (3) becomes more and more pro- 
minent as y increases in value. It will therefore be sufficiently 
accurate in the first instance to consider the fundamental period 
only and to assume that it causes in the skin of the metal a 
fluctuation of temperature of much the same nature but of 
less amplitude and with at least some lag. What this ampli- 
tude and lag will be it is impossible to calculate, but it is pos- 
sible to take the extreme case in which the range of temperature 
in this skin is equal to that in the gas. This at least will repre- 
sent the limit of what can occur in that direction. Then 6 = C 
sin yt is the equation for the temperatures both of gas and 
skin. 

74. Effect at a Depth. — It remains to investigate how the 
rest of the metal wall is affected by this great vibration in 
temperature in one of its faces. It is clear from equation (3) 



94 THE INTERNAL COMBUSTION ENGINE [chap, iv 

that the amplitude decreases with the depth in the metal and 
that a lag arises and increases at the same time. The amplitude 

at any point at a depth x is C exp.( — \/ l ^ZT x \ j^ q j s ^e 

2k 
amplitude at the surface, and therefore the fractional amplitude 

in the interior is exp. ( — \/ WT Y x ) 

V 2k . J ' 

It is of interest to evaluate this expression. 

We may put w = 450 lb. per cubic foot ; y = 1Q- corre- 
sponding on the basis of a two stroke cycle to a speed of 
300 r.p.m. ; <t = 0-1 ; k = 0-01. So that 

W °l = — ^XO-IXIOttX 100=70,500 

2k 2 



/wTy_ [ 



or a/— -=266 

X 2k 

and the fractional amplitude == e~' 26Qx 
here of course x is in feet. If x be put equal to J in. or 

xVfoot, the fractional amplitude = . .„ = or 0-40 of one 

4 8 v e o. o3 250 

per cent., which shows that even at a depth of only J inch the 
temperature oscillation is practically wiped out. The curve 
in Fig. 28 shows graphically how rapidly the oscillations de- 
crease in amplitude. So that in assuming the wall to be in- 
finitely thick no very far-reaching assumption was made, since 
for anything over J in. in thickness the temperature on the 
water side will practically show no temperature oscillation. 

75. Conclusions. — This mathematical investigation shows 
that the temperature gradient from face to face of the wall is 
practically unaffected by the oscillation in the temperature of the 
gas, and that if to this gradient line the above shallow tempera- 
ture oscillations be added a representation can readily be ob- 
tained of what is actually occurring in the walls of a gas engine 
cylinder. The heat flow through the metal is known, as regards 
quantity, from the heat balance-sheet for the engine, since the 
heat taken away by the cooling water must be exactly equal 
to the flow through the walls if a steady state has been reached. 



CHAP. IV ] 



THERMODYNAMICS 



95 



The difference in temperature between outer skin and water 
must just be enough to enable this amount of heat to pass. 
In a 10 in. X 18 in. two stroke engine which loses say 
30 H.P. continuously through the walls of an exposed 
area of 4 sq. feet, the average temperature gradient* will be 



- 1 



— x 10=25° C. per inch. If the inner skin be at an average 
temperature of 200° C, then the outer skin would be at 175° C. 



1-0 



0-3 



08 



0-7 



06 



5 0-5 
u 

« 



0-4- 






03 



02 



0-1 



































































































































I 

1 
j 


























































i 

iH — 







-025 



■05 



•075 



0-1 0125 015 0175 0-2 0-225 025 
oc'= Inches depth in Metal. 
Fig. 28. — Showing amplitude of temperature oscillation in an infinite block 
of metal when the skin temperature oscillates above and below the mean 
temperature of the block. 

From the equations of par. 72 it is possible to calculate the 
flow r of heat through the inner skin into the metal during the 
period of time (i.e. the explosion stroke) in which the skin 
temperature is greater than that of the mass of the metal. 

* A plate of average iron, having a temperature gradient of one 
degree Cent, per inch of thickness, will steadily transmit per square 
foot of area about T 3 ^ horse power, 



THE INTERNAL COMBUSTION ENGINE [chap, iv 
Thus the heat flow at the surface must be — k[ — ) 

= I . C -in yt-\-cos yt] —k . a . C - V2 sin (}^+— )- 

The amount of heat flowing per sq. ft. between times 1 = o 

and /=-inust be= J t i vl s _■ im ( yf_|— ) . dt=~— . Insert - 

^ 4' y 

ing the values of the constants of the previous paragraph 

we have heat flow =2 001 X266xC ^ ^^ for 

10- 

example a heat loss equivalent to 7 J H. P. per sq. ft. of surface, 

jj "11 

then heat flow in one cvcle (at 300 r.p.m.) = 7-5 X X 0-2 

1400 

= 0-59 pound-calories, which may be equated to 0-1 7C. giving 
= 3-5 deg.. or a total temperature oscillation of 7 degrees. 
This indicates generally that a small oscillation in the tempera- 
ture of the innermost layer of metal is quite sufficient to absorb 
and level the temperature oscillations which the gas tends to 
-r~ up in the evlinder walls We mav conclude from this that 
although the temperature at any point of the walls depends 
on the position of that point, it does not sensibly vary with the 
time : that is to say, that at any given point the temperature 
in the walls remains nearly steady. The wall may therefore 
be considered as of two parts — the inner skin which acts as 
an accumulator of heat energy, rapidly abstracting it during 
explosion and giving it out again later : and another part, 
consisting of the whole of the rest of the wall, which acts ae 
a -ready transmitter of the heat fed into it through the inner 
layer. 

76. Heat Paths. — A simple picture can now be drawn of the 
manner of heat flow in a gas engine cylinder : heat passes tc 
the walls by convection and radiation : this is facilitated by 
the cooling of the walls by the water circulation. Heat 
flows most freely into those parts of the metal which are in the 
explosion space. Valve seatings. ignition bosses, and parts 
supported by webs tend to get hottest, as the water is more 
remote and the heat has less chance of escaping. The main 






chap, iv] THERMODYNAMICS 97 

heat How is straight through the metal of the wall, but it also 
passes along it if the water supply be not copious. A certain 
amount of heat passes into the piston face. This escapes in 
two ways — out at the back of the piston, and radially to its 
edge and along the trunk. All these heat paths require study, 
so that proper allowances can be made for the expansion of 
the metal. Ignorance of the Avay in which this expansion 
occurs has led to the cracking and failure of a great number of 
cylinders. 



EXAMPLES 



1. The temperatures on the two sides of an iron plate 0-5 in. thick 
differ by 10° C. How much heat in C.H.U. passes through per sq. ft. 
per minute ? Conductivity of iron is 0-0074 C.H.U. per sq. ft. per 
sec. for each degree Centigrade drop of temperature per foot of travel. 

2. A gaseous mixture has a specific heat at constant pressure of 0-26 
and one at constant volume of 01 9. J = 1393. 

(i) What is the law of adiabatic expansion ? 

(ii) If a pound of it is at 120° C, pressure 5000 lb. per sq. foot, w^hat 

is its volume ? 
(iii) A pound of it expands according to the law PV* = constant ; 

what is its rate of reception of heat in C.H.U. ? 

[B. of E., 1899.] 

3. The characteristic equation for the expansion and compression 
of one pound of air is PV = 96 T, 

where P = pressure in lb. per sq. ft. 

V = volume in cu. ft. T = temperature abs. in degrees 
centigrade. 

One pound of air expands from an initial pressure of 50 lb. per sq. inch 
abs. to a pressure of 20 lb. per sq. inch abs., the corresponding change of 
volume is from 4 to 15 cu. ft., and the mean value of the pressure during 
the expansion (as deduced from a diagram) is 32-7 lb. per sq. inch. 

Calculate — 

(i) The initial temperature. 

(ii) The final temperature. 

(iii) The change in internal energy and the heat received or rejected 
during the change from the initial to the final condition. 

[C, = 0-169.] 

[B. of E., 1912.] 

4. Air is compressed adiabatically from 15 to 700 lb. per sq. inch in 
two stages, the air being cooled finally, and also between the stages to 

H 



IJIB OTKRIXAL C 7 II zap rv 

tfee- nriitTTTiJi teeniMmJriUiWLr. wMeSl is- 1&° C Calculate the inter - 

sore wBwA lil nn worik dbne a m HiimunL. afae the work c 

:er - : •._: md lie lenr rimed i-vq- :n :Ie :•:< _m: ~ir r r 

: ;- - r—rs : -n ; 

■ ■ . - 

".' \-_'\ ■ ~*r : ~:Z ' -' '■''CC. .■ -.---.-— LZ.-1 T-iemiil*. '• T ;.t . 7'-: -11_~ "" . 1111 ■- 

■ - _- igwigBgHsfcHire at ttr~ - " " lie distance x from 

sonfeefe. Stfcet rr - -snjft^frBBw of this equation . - 

IT = T' n er aas <ic!r - - 

- _ - • : -rare «£E aennf-rci i 

- bean" lia? amgife dieseiafcedi fejr tifc@> cranfe in time :_ r 

- _ .. . - I - .. - ir - - . Prove - 

inns inifex caeflnsieii-- - ami find the b 

afegGmfceffiikitnerni^Tiiaife 

-. -i -rizi^e i~ :Ie fiinli'je :e"~:g 

.7 •: 7 : 

Si. TwT5>e^B^aBJgg^feeweM^€JiaHTgR^t@^^^aitggP £ aEEdf . 

\n : l." ".._- -•'._!_- : -i- :--:■■. "iz - f ir-f ■ i_i- ~-i :~ • -- :-.'._-i 71- 

: fried m - :-_..:-. — ed. 

■ _l_ ■ loss atf laear a - iji itli wm -nnswr that tne presson© 

- - - : 



~ 1- 



iniT --":"-:"._- 



- 

leasl i qpawtiit - " — m astr Taflnanately fee- wasted - 3eing the 

- -if " - "._ . - : " r- 
At*- i -:_,•__- - \.l-- m 3M>1bJir.afr I r > aa) re - la its hear 6 

IseB^r wfease- tewopeBater - :i.— - 1 i -r o Th,U. of heat ahsor- 

7 - : ■ _• - :-..--•'-"-- ._- " -hat the h 

zi-zri v :ii — _ ■ .1 :Iie -/__-__- -in i ..- 113 77_ "1" m<: :Iiir :Ie in ■. 
--:._:►-:■ \—-- : due :«:d— — 1_ lien :e rii ; 1 

7 7 - 7 : ■ . . ; 

-- -i- : i~ ~ :~ rf ^:_ic£ gg mitimf] i : .ffflajeesatiire. Its plane 

feee or = a is saiiienljr nansed to tempeiaitar - - 
thac temperacure^ Sio w thait a&eir £ seconds literature i 

i : i,LC z - :: : --- . ;_ : : -._- --z^Tiera- 

"■-- v -~ - : " ■ ■ " -._:._- ' -.;. - :f_m-er " .j- _■?•■._ - 



chap, iv) THERMODYNAMICS 99 

surface x— o is . - where a = — , k being the conductivity, c the 

specific heat, and /> the density of the material. 

[Mech. Sc. Tripos, 1912.] 
9. A quantity of heat Q per unit area is suddenly communicated to 
the plane face of a solid slab of great thickness. Prove that the tem- 
pt rat ure / seconds later at a depth x within the solid will be 



IXZ 



«Q v/_£_ e Akl 

N kl 

where k is the thermal conductivity, e the thermal capacity per unit 
volume, and o a constant. 

Plot a curve on any convenient scale showing the temperature distri- 
bution in the solid at any time, and show from this curve that a = 
0-565 nearly. 

[Mech. Sc. Tripos, 1911.] 

10. Draw the entropy-temperature diagram for an ideal gas-engine 
working on the Otto cycle, and compare it with the similar diagram of 
the same cycle when the specific heats are functions of the temperatures 
given b} r C„ = ft -\- sr. C p — a -\- sr, r being the absolute temperature. 
Compare the efficiencies in the two cases. 



SECTION II 
GAS ENGINES AND GAS PRODUCERS 



CHAPTER V 

The Gas Engine 

Modes of Action — Types of Engine — Humphrey Gas Pump- 
Gas Turbine — Methods of Improving Efficiency — Indicators 
and Indicator Diagrams — Heat Balance Sheets — Engine 
Tests — Governing — Cyclic Irregularity — Balancing. 



77. Modes of Action.— The three ideal cycles of operation 



are 



(1) Constant pressure cycle. 

(2) Constant volume cycle. 

(3) Constant temperature cycle. 

And an engine working on one of these may be either a 

(1) Two-stroke engine, or 

(2) Four-stroke engine. 

And it may further be either : — 

(1) Single-acting, or 

(2) Double-acting. 

This leads to a considerable variety of types, although fully 
80 per cent, of the internal combustion engines in the world 
work on the constant volume cycle, are four-stroke and single- 
acting. The various combinations are set out in the following 
table, and the names of the more important of the representa- 
tives of each class are given. Some engines, such as the 
Humphrey Pump, and Gas Turbines, do not fall into any 
distinct class. 

103 



104 THE INTERNAL COMBUSTION ENGINE [chap, v 



Internal Combustion Engines 



1 

Constant Pressure Cycle 
1 


Constant 

1 

'-stroke 

1 


Volume Cyc 


1 

e Constant Temp. 
Cycle (not used) 


1 

Two-stroke 

1 


Foui 




. 1 1 

Single- Double 
acting acting 
(Diesel 

oil 
engine) 


. 1 

Single- 
acting 
(Diesel 

oil 
engine) 


1 

Double- 
acting 




Two-stroke 

(Clerk cycle) 

1 


Singl 

(most 

form 

oil, pet 

Manj 


Four- 

(Otto 


1 

stroke 
cycle) 
1 


1 
Single-acting 
(Oechelhauser 
gas engine and 
some petrol 
engines) 


1 

Double-acting 

(Koerting gas 
engine ) 


1 

3-acting 

common 
of engine, 
rol or gas. 
t types) 


1 

Double-acting 

(Cockerill and 

several other 

large gas 

engines) 



The relation between the maximum number of explosions per 
minute and the number of revolutions per minute depends upon 
the class to which the engine belongs. The four- stroke single- 
acting engine has one explosion, and therefore one working 
stroke for two engine revolutions ; the four-stroke double- 
acting and the two-stroke single-acting engines have one 
explosion per revolution, and the two-stroke double-acting 
engines two working strokes per revolution, as in the case of a 
steam engine. 

Practically all gas engines work on the constant volume 
cycle, sometimes two-stroke but more often four- stroke ; the 
former is commonly known as the Clerk cycle and the latter 
the Otto cycle, from the names of those who first suggested 
them. 

78. Typical Otto Cycle Engine. — A typical instance of the 
well-known Otto cycle gas engine is shown in section in Eig. 
29. Gas and air enter through the casting G, and pass the 
inlet valve A (operated by cam arrangements not shown in 
the figure). As the gas and air enter, the piston C moves 
along the cylinder, being drawn by the connecting rod D 
attached to the crank-shaft E. After the gases have been 



CHAP. V] 



THE GAS ENGINE 



105 



allowed to fill the cylinder they arc compressed on the return 
stroke of the piston, are ignited on the inner dead-centre, 




I 



a 

'3d 
a 
H 

w 
oS 

O 

© 

o 

o 

H 



6 

M 



106 THE INTERNAL COMBUSTION ENGINE [chap, v 

expand doing work, and on the exhaust stroke the exhaust 
valve B opens to allow them to escape into the silencer. The 
cylinder is kept sufficiently cool, to enable it to be lubricated, 
by means of a circulation of water in the jacket space F. 

79. The Origin of the Clerk Cycle. — This cycle was invented 
some years after the Otto by Dugald Clerk, who gave the 
following description of it to the Society of Arts in 1905 : 
" In the Clerk engine the motor cylinder had, at the front ends, 
large ports leading into an annular space, these being the 
exhaust ports. The compression space was conical, and the 
charge was sent in by means of a separate pump, which I 
called the displacer. The action of the engine was as follows : 
When the piston got to the out end of its stroke, and the 
crank was crossing the out centre, the piston overran the 
exhaust ports on the out-stroke, and covered them on the 
in-stroke. Meantime the pump or the displacer piston, which 
was attached to a crank at right angles in advance of the main 
crank, was sweeping in and giving its charge a slight compres- 
sion. That charge passed through a connecting pipe, and 
through a check valve, into the conical end, displacing before 
it all the contents of the cylinder. When the main crank had 
returned about 40 degrees of its circle under the centre, these 
ports were closed. It opened about 40 degrees above and 
closed 40 degrees under, and in that time the displacer piston 
had gone fully in and discharged its charge into the cylinder 
and combustion space through the lift valve. Then the 
motor piston compressed the charge, and ignition took place 
at the in-end of the stroke, just as in the Otto cycle. The 
object of the invention was to enable one motor cylinder to 
give an impulse at every revolution. In the Otto cycle there 
is only one impulse for two revolutions, so far as the main 
cylinder is concerned. The Clerk engine gave one impulse 
for every revolution of the main crank in the main cylinder, 
but to make that possible it was necessary to provide an 
auxiliary crank and displacer cylinder.* The idea was, of 
course, to diminish the irregularity of the Otto cycle by having 

* Crankcase compression is now generally adopted for small two- 
stroke engines, thereby avoiding the necessity for a separate displacer 
cylinder. 



CHAP. V] 



THE GAS ENGINE 



107 



an impulse at every revolution, or more frequently, thai is to 
siv. two impulses per revolution, obtained by making the 
engine double-acting. The object was to get very much more 
power for a given weight of engine, as the pump was light 
and only required to deal with its charge at a low pres- 
sure." 
80. Large two-stroke Engines. — There are two well-known 



1 1 




C 
1 1 


B 2 

_J L 


1 




/ 
1 


- A 


! \ — 


_i 


_j 




-i 


— 0" - 


— — 


r 


i 



Fig. 30. — Diagram of Koerting Engine. B x and B n Inlet Valves ; C Exhaust 

Valve. 



designs of large two-stroke engines, both German in origin, viz., 
the Koerting and the Oechelhauser. The former is double- 
acting and the latter single-acting. In the Koerting engine, 
illustrated ^grammatically in Fig. 30, the piston A is unusually 
long, and by alternately covering and uncovering the exhaust 
port C is itself a part of the valve gear. The mixture of gas 
and air is admitted alternately at B x and B 2 from the pump 
cylinder. If there has just been an explosion at the left-hand 
end of the cylinder, the piston will move to the right, and the 
gases will expand, doing work. By the time the piston has got 
to the end of the stroke, it will have uncovered the exhaust 
port C, and the burnt gases will rush away. At this point 
the inlet valve B 2 is opened, and fresh air and gas are pumped 
in. This fresh charge is compressed on the return stroke of 
the piston, and ignited, as before, on the dead point. The 
same cycle of events goes on at the right-hand end of the 
cylinder, so that there is an explosion at the right-hand end 
when C is uncovered in the left-hand end and vice versa. 
The piston receives therefore just as many impulses as a steam 
engine piston. 

An obvious difficulty about this method of working is that 
some of the incoming gas may be caught up by, and pass 
away with, the exhaust products and be lost. This reduces 
economy, but is of little importance when working with what 



108 THE INTERNAL COMBUSTION ENGINE [chap, v 




u 
o 



© 

— 
_G 

© 

© 

o 
ft 



ft 

•S o 



fc£) 

G 

_© 

-3 
G 
c3 



>> _, 





- 


^L. 


© 




+3 

03 


— 




- 


w 


i. 


© 





> 


M 


03 




S> 


(V) 




G 

"3c 


4-> 


- 




W 


o 


c 


-t-J 

o 


u 


z; 


u 




o 




£ 


£ 


H 


o 






«4H 


» 


O rQ 


G 


ft 


o 
o 


- 


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— 


7 






Sh 






- 


<J 


- 




— 


— 


- 


- 

03 






bxi 


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C 


03 


o 


" 


h-l 
l 




1 


© 


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> 


PC 


O 




_: 


o 


03 



CHAP. v| 



THK GAS KXUINK 



109 







>> 






a 
o 

w 

> 

> 
-p 

CD 

3 



o 

6 



^j CD 

© d 

<3 d 

^ o 



© 
d 

'So 

d 
H 

CD 

o3 

o 

bO 

d 



O 



o 
o 
ro 

I 

CO 

C 

H 



are known as ^as^e gases * as these are produced in immense 
volume and at practically no cost. 



* See Ch. VII. 



110 THE INTERNAL COMBUSTION ENGINE [chap, v 

Attention has been given in the previous chapter to the 
question of piston and cylinder wall temperatures, and it will 
therefore be readily understood that in such a cycle as this 
the heating effect of explosions so closely following each other 
will be severely felt and high temperatures are likely to be 
reached by all parts open to the gases. 

In the Oechelhauser engine shown in Fig. 33, there are two 
pistons which are so connected to the crank-shaft as to move 
alternately towards and away from one another. Air is 
admitted from the pump cylinder through the holes C, in the 



RCR 



r. D 



*o o 
oo 
oo 
oo 
oo 



OCR 




RCR 



Fig. 33. — Diagram of Oechelhauser Engine. D C R direct Connecting Rod ; 
RCR two Return Connecting Rods ; Air enters by Holes at C ; Gas 
at D ; Exhaust leaves at B. 

walls of the cylinder, and gas through the holes at D as the 
piston, A 2 , uncovers them in turn. The mixture is then 
compressed between the two pistons as they come together, 
ignited at the dead point, expanded during the expansion 
stroke, and then exhausted by the uncovering of the exhaust 
port B. The engine is single-acting so that only half the 
horse-power is obtainable as compared with a Koerting engine 
of the same cylinder dimensions. The piston A 2 works 
directly on to the crank-shaft as shown, but the piston Aj 
has to have a separate cross-head and two long return connect- 
ing rods. The balancing is good, as the two heavy pistons 
balance one another. The Gobron-Brillee and an early form 
of the Arrol-Johnson motor car engines worked in much the 
same way. The engine invented by H. F. Fullagar * and 



* H. F. Fullagar, Proc. I.M.E., 1914. 



chap. v| 



THE GAS ENGINE 



111 




ft 



O 
00 

C 
o3 



O 

bD 
C 



M 



03 

C 

P 



T3 
o 



£P 



o 
O 

o 
o 



M 

ft 



112 THE INTERNAL COMBUSTION ENGINE [chap, v 

known by his name also bears a general resemblance to the 
Oechelhauser type. 

That there are difficulties to be overcome in the con- 
struction and working of large gas engines, particularly those 
working on the two-stroke cycle, is shown by the history of the 
generating station for lighting and tramway work which was 
established some years ago at Johannesburg. The plant was 
operated with Oechelhauser gas engines driven by gas from 
Poetter producers using Transvaal coal. Erom the beginning 
many difficulties arose in the operation of this plant, mainly 
on account of the lack of requisite experience in the manu- 
facture and operation of similar installations. The cost per 
unit is reported to have been higher than was anticipated, and 
the plant has since been shut down. This occurrence must 
not be taken to show that Oechelhauser engines are unsuitable 
for heavy work, since in numerous places on the Continent 
engines of this make are working well. 

A large installation of gas engine plant in this country is 
that at the Cargo Fleet Iron Co.'s works at Middlesbrough. 
It consists of six Cockerill engines, built by Messrs. Richard- 
sons, Westgarth & Co., of 900 H.P. each, or a total of 5,400 H.P. 
These engines work on the Otto cycle, but by having double- 
acting tandem cylinders the crank gets just as many impulses 
as in a double-acting steam engine. 

81. Other Types of Engines. — There are a number of British 
and foreign makes of engine (e.g. the Ehrhardt and Sehmer 
engine) which work on the four-cycle double-acting principle, 
giving an explosion per revolution for each cylinder, so 
that for two cylinders placed tandem every stroke is a 
working stroke just as in a steam engine. With the tandem 
arrangement there is the advantage that the motion towards 
each dead centre is always accompanied by a compression 
stroke ; this leads to a cushioning action which is useful as an 
aid to overcoming the inertia effects- due to the moving parts. 
Engines of this type have met with much success, thus Mathot,* 
writing in Gas and Oil Power, stated that : •■" A 600 H.P. double- 
acting Ehrhardt and Sehmer engine, with two tandem cylin- 
ders, was tested, without previous cleaning, after four months' 

* December 15, 1906. 



chap, v] THE GAS ENGINE 113 

continuous work with coke-oven gas of from 4,000 to 4,200 
calories ; the trial was carried out by the makers' engineers 
under the supervision of Kgl. Berginspection's engineer. 
Thanks to a large gasometer, the record of gas consumption 
was taken for a period of one hour. The mechanical efficiency 
was 83 per cent. The engine was new and was tested on a 
normal load. The dimensions of its pistons and piston rods 
were respectively 620 mm. and 170 mm., 750 mm. stroke, 
and 150 revolutions. It just reached 520 KW., generating 
three-phase current. In the conditions of the trial the actual 
thermal efficiency was more than 31 per cent., or nearly 37 J 
per cent, of that indicated. Unfortunately, similar trials to 
this are rare because gasometers are not usually sufficiently 
large to measure the exact amount of gas used by the engine." 
Another well-known type is the Premier gas engine. Perhaps 
its most familiar feature is the scavenging of the exhaust 
products by means of an air blast. It has been stated that 
this blast is capable of keeping the cylinder interior almost 
free from deposit even when working with bituminous fuel 
gas plant. An account has been published * of a 1,200 H.P. 
four-cylinder gas engine by the Premier Gas Engine Co., 
which was constructed for direct coupling to a continuous 
current generator and consisted of two sets of tandem cylinders 
working on cranks set at 180 degrees apart. A four-stroke 
cycle was employed, so there were two working strokes per 
revolution. A scavenging charge of air supplied from a 
separate air cylinder at about 3 lb. per square inch was used 
to clear the cylinders of waste products. All the valves 
were placed on the cylinder covers ; pistons and exhaust 
valves were both water-cooled. It was stated that, operating 
on producer gas, a compression pressure of 140 lb. per square 
inch could be used without any difficulty whatever from pre- 
ignition, and that a test on the engine showed the mechanical 
efficiency to be as much as 87 per cent. 

82. The Humphrey Gas Pump. — One of the most remarkable 
applications of the internal combustion principle is seen in the 
gas pump invented by H. A. Humphrey, and described by 
him at a meeting of the Institution of Mechanical Engineers 

* Engineering, Jan. 11, 1907. 

I 



114 THE INTERNAL COMBUSTION ENGINE [chap, v 

in 1909. Its chief feature is the use of a swinging column of 
water in place of piston and connecting rod, the upper face of 
the water column taking the place of the piston face. 

The following extract from the inventor's description * 
makes his purpose clear : — 

" The idea of exploding a combustible mixture of gas and 
air to produce pressure on the surface of water, with the object 
of raising the water, is of course not new, and attempts to put 
this idea into practice date back to 1868. The efforts have all 
been directed too much along the lines of ordinary pumps, in 
so far that the water lifted has always been forced past a non- 
return valve, and the operation of such a valve with the 
explosive force behind it has been inevitably disastrous. In 
the types of pumps invented by the author there is, when the 
explosion occurs, a full-bore passage from the combustion 
chamber to the final outlet, also some of the water pumped to 
a high level by the energy of the explosion is allowed to return 
again to compress a fresh combustible charge. When sudden 
changes of velocity occur in masses of a heavy and incom-' 
pressible liquid, like water, great difficulty is found in con- 
trolling the movement of the liquid. All such difficulties are 
removed in the author's pumps by allowing the movements of 
liquid to control the pump, and by causing the mass of liquid 
moved to be sufficiently large, so that the velocities are never 
excessive. The mass of water forms a pendulum which swings 
between the high and low level, and, by its movement alone, 
serves to draw in fresh water, to exhaust the burnt products, 
to draw in a fresh combustible charge, and to compress the 
charge previous to ignition. With the movements of the 
liquid quite unrestrained by any of the usual mechanical 
appliances, the result is a pump which works with freedom from 
shock and noise, and which requires very few working parts. 

" The subject attains a wider scientific interest from the fact 
that the apparatus follows a cycle in which the expansion of 
the burnt products is carried to atmospheric pressure, and so 
involves a thermodynamic cycle of greater efficiency than can 
be claimed for the Otto cycle." 

It is stated that the pump is suitable for working with 

* Proc, I.M.E., 1909. 



CHAT. V | 



THE CAS ENGINE 



115 




3 
ft 

a 

9 

W 



«2 

CO 

d 

H 



producer gas, suction gas, lighting gas, petrol or paraffin ; 
there are no moving parts except the interlocked inlet and 



116 THE INTERNAL COMBUSTION ENGINE [chap, v 

exhaust valves to the combustion chamber and the outlet 
valves from the suction water-tank. The use of a flywheel is 
not necessary, since the reciprocating water column performs 
also the flywheel function. 

The cycle followed is a constant volume cycle, but the 
strokes are not all of equal length. The strokes are, (1) a 
long stroke during explosion and expansion, (2) another long 
stroke during exhaust, (3) a short stroke during suction, and 
(4) a still shorter stroke during compression. 

A simple form of this pump is shown diagrammatically in 
Fig. 35. 

Imagine a charge of gas and air to be compressei at the 
top of the combustion chamber in the space shown and let it 
be fired by a sparking plug, not shown in the diagram. The 
explosion pressure drives the water out of the combustion 
chamber and sets the whole water column in the discharge 
pipe in motion. As the gases expand the kinetic energy of the 
moving water steadily rises, until the gases arrive at atmo- 
spheric pressure. There is then no further driving force on the 
water column, but owing to its kinetic energy it continues to 
move forward and the pressure in the combustion chamber 
sinks below the atmospheric pressure, so opening the 
exhaust valve and the water outlet valves from the suction 
tank. Water rushes from this tank into the discharge pipe 
and into the combustion chamber. When the kinetic energy 
of the moving column has entirely expended itself in forcing 
water into the delivery tank and in overcoming the friction 
due to its motion, it comes to rest and gradually starts to 
swing back again until it rises to the upper part of the com- 
bustion chamber and closes the exhaust valve by impact. 
Its further motion is arrested by the cushioning effect of the 
burnt products trapped in the compression space, and gradually 
the water-pendulum begins to swing back again, opening the 
inlet valve and drawing in a fresh explosive charge which on 
the return swing of the water is compressed, and, at the 
dead-point, fired, so bringing a fresh cycle of events into 
operation. Thus the pumping continues. 

A test by Unwin in 1909 showed a consumption of 1-063 lb. 
of anthracite in the producer per pump H.P. hour correspond- 



chap, v] THE GAS ENGINE 117 

ing to 12.243 B.Th.U. per P.H.P. hour, a very satisfactory 
result. A large battery of these pumps was subsequently 
erected at the Chingford Reservoir * under a guarantee that 
not more than 1-1 lb. of anthracite per P.H.P. hour would be 
consumed. Later still a very large plant has been constructed 
for Egypt f ; eighteen pumps will be needed, each capable of 
delivering 100,000,000 gallons per day through a lift of 20 it. 
The combustion chambers are 8 ft. 8 in. in diameter and 
about 14 ft. high. 

83. The Gas Turbine. — The great success achieved by the 
steam turbine has naturally led inventors to make numerous 
attempts to devise a gas turbine, and so to reap the joint 
advantage of the high thermal efficiency of the gas engine 
and the even rotary motion of the steam turbine. A gas 
turbine may be defined as a turbine in which a gas, usually 
a product of combustion, with or without an admixture of 
steam, is the working medium. This medium suffers, however, 
from the disadvantage that it is not condensible as is steam, 
and it is not therefore possible to obtain the " toe of the 
diagram " unless the exhaust products are drawn out by a 
pump (in which event care has to be taken that the gain due 
to increased expansion is not overbalanced by the work of 
pumping). 

Gas turbines are divided into two main types, those in 
which combustion occurs at constant pressure and those in 
which it occurs at constant volume ; the latter are known as 
explosion turbines. Hybrid machines operate on an inter- 
mediate cycle and share the features peculiar to both. 

Much of the difficulty in all types of turbine is the burning 
of the blades owing to the high temperature of the gases. This 
temperature is reducible by the addition of steam, but unless 
this steam is afterwards condensed the latent heat in it is 
lost. 

The number of gas turbines hitherto built is very small. 
The first, due to Rene Armengaud, was begun about 1904, 
and gave as much as 300 B.H.P., but the efficiency was very 
low. It operated on the constant pressure method. The 

* Engineering, February 14, 1913. 

t Internal Combustion Engineering, June 24, 1914. 



US THE INTERNAL COMBUSTION EXGIXE [chap, v 
next in order of time was the little explosion turbine, giving 

J. CO 

less than 2 H.P.. designed by Karovodine : despite its small 
size it promised well for small unit work. The third was the 
1.000 H.P. explosion turbine of Holzwarth's which met with a 
fair amount of success, although it did not yield more than 
half of the 1,000 H.P. it was designed to give. 

Dugald Clerk * thinks there is little chance for the constant 
pressure turbine, but that better prospects lie before the type 
of turbine in which successive gas explosions propel jets of 
water against the vanes of a water turbine and in which 
there is therefore no contact of name and blade. Norman 
Davey t considers on the other hand that blade temperature, 
even when in direct contact with flaine, can be kept within 
manageable limits, so offering prospect of success for a 
constant pressure mixed (steam and gas) fluid working at 
very low pressures. 

Modern steam turbines work with steam which is highly 
superheated and which is therefore in the state of a gas and not 
a vapour. Such turbines may therefore be called gas turbines, 
although not on the internal combustion principle. Such 
"" external combustion gas turbines." if so they may be called, 
may prove too successful for the competition of the internal 
combustion turbine, especially if, owing to the great improve- 
ments being effected in steam boilers, the efficiency of the 
latter can be brought up to the level reached by the gas- 
producer. This question formed a part of the subject of Fer- 
rantfs "'James Watt Lecture." J and the following extract 
is quoted : — 

" The speaker began experimenting some years ago, and 
had now, after many failures and the expenditure of much 
money and time, produced a turbine which at the highest 
temperatures and with great and rapid variations of tempera- 
ture was quite free from mechanical troubles. 

"La this turbine the steam was superheated initially, and 
after the first expansion and while it was still superheated it 
was re- superheated before it did its work in the second stage 

* British Association, 1912. 
f The Gas Turbine, 1914. 
: Times, January 22. 1913. 



chap, v] THE GAS ENGINE J 19 

of the turbine. After this it was exhausted in a superheated 
condition through a regenerator to the condenser. The whole 
of the blading was electrically welded to avoid the straining 
due to caulking at the high temperatures that were reached 
and also the loosening that occurred from the same cause. 
The blading was formed of mild steel with a thin coating of 
pure sheet nickel electrically welded on the surface, was most 
accurately finished to shape by a process of step-by-step 
pressing under very heavy pressure, and was welded accurately 
in position. 

" The steam was worked as a gas at a high temperature 
throughout the turbine, and this coupled with the many 
improvements above referred to had given very good results. 
The 5,000-H.P. machine, which had now been running for 
some time, when tested at a load of two-thirds full power had 
given a shaft H.P. on 7 lb. of steam which, if supplied by an 
oil-fired boiler superheater system of 85 per cent, efficiency, 
which had already been exceeded in central station practice, 
would consume less than -625 lb. of oil per S.H.P. From many 
tests already made it appeared that when it was run at full 
load under favourable conditions it would take less than 6 lb. 
of steam per S.H.P. , and that the system under the conditions 
named Avould have a thermal efficiency of over 24 per cent., 
corresponding to an oil consumption of about -55 lb. of oil 
per S.H.P. The tests were being continued, but as the turbine 
was supplying power continuously to a large works with a 
constantly varying load, it was not easy to do what was neces- 
sary to enable tests to be carried out. So far as he could 
see, the system, when applied on a large scale, would be 
capable of giving an over-all thermal efficiency of 29 per 
cent." 

84. Methods of Improving Efficiency (Crossley and Na- 
tional). — One of the chief causes which limit the efficiency of 
gas engines is the high temperature during explosion and the 
very rapid rate at which heat is then abstracted by the 
walls. Two methods have been tried with a view to 
minimize this effect, the idea in each case being to reduce 
the maximum temperature of the cycle Without, however, 
decreasing the mean pressure. These two are the water 



120 THE INTERNAL COMBUSTION ENGINE [chap, v 

injection method of Messrs. Crossley Bros., and the super- 
compression method of Dugald Clerk. 




^~" 




Fig. 36. — Campbell Gas Engine. Note the disposition of the inlet and ex- 
haust valves, and the water cooling arrangements. On the plan at the 
lower side is seen the half-time-shaft. 

85. The Water Injection Method. — Messrs. Crossley decided 
to try the effect of injecting a small spray of water into the 
cylinder during the suction stroke. The water, entering as a 
fine spray in part of the air supply, was as evenly distributed 
as possible and did not form a water film on the cylinder walls. 



CHAP. V] 



THE GAS ENGINE 



121 



Very little water is required, because of the high value of its 
latent heat. As the mixture explodes the water mist is 
evaporated into steam and the heat so absorbed prevents the 
temperature of the gases from rising unduly high. A 50 H.P. 
engine so adapted was tested by Professor Burstall in 1904 
and the following records taken : — 



Size of engine 


. 14 in. X21 in. 


Average revs. /m in. 


. 16602 


„ I.H.P. . 


60-5 


„ B.H.P. . 


49-7 


Mechanical efficiency . 


82-2 per cent. 


Gas used per I. H.P. -hour 


. 11-77 cu. ft. 


„ B.H.P.-hour . 


14-43 „ 


Calorific value of gas (lower value 


) 578B.Th.U. per cu. ft 


Thermal efficiency on I.H.P. 


37-43 per cent. 


„ „ ,, B.H.P. 


30-8 


Water used in cylinder : 


0-131 lb. per minute 


„ discharged from jacket 


25-66 


Mean temperature of exhaust as 




measured by Callendar pyro- 




meter . 


718° F. 



The ratio of air to gas was 10-2 and the compression ratio 
8-7, corresponding on the " air standard " to an efficiency of 
0-58. As the actual efficiency found was 0-37 it follows that 
the engine achieved nearly 64 per cent, of the " air standard ' 
efficiency. This is a higher ratio than any of those given by 
Dugald Clerk in his 1907 paper before the Institution of Civil 
Engineers (" On the Limits of Thermal Efficiency in Internal 
Combustion Motors "), which showed no higher ratio than 
59 per cent, and that only in the case of a maximum tempera- 
ture of 1,098° C, whereas when the temperature rose to 1,750° 
the ratio fell to 50 per cent, and below. On this method of 
comparison, therefore, the w r ater injection method shows to 
advantage. 

Water injection has been tried on a still more extensive 
scale by B. Hopkinson,* who used it to replace entirely the 
usual water jacket system. The work of the Gaseous Explo- 

* " A new method of cooling gas engines," Proc. I.M.E., 1913. 



122 THE INTERNAL COMBUSTION EKGINE chap, v 

sions Committee had shown that almost the whole of the 
cooling loss occurred during and immediately afterthe explosion, 
and that the cooling of that part of the cylinder walls which 
did not form part of the combustion space was chiefly useful 
in keeping the piston cool (since unless the circumference of 
the piston were kept cool the centre might rise in temperature 
to the pre-ignition point), so that if a jet of water could be 
projected on to the hot face of the piston and on to the walls of 
the combustion space it might be possible to dispense with any 
other cooling arrangements altogether. This makes for great 
simplicity in construction and corresponding economy in 
first cost. 

In Hopkiuson's engine cold water is injected through a 
hollow casting projecting into the combustion chamber and 
provided with a number of holes or small nozzles rather less 
than a millimetre in diameter. The jets thus formed are 
comparatively coarse, and even after passing through the flam- 
ing gas most of the liquid reaches the hot metal surface upon 
which it is directed. These jets are directed against all parts 
of the surface of the combustion chamber and against the 
face of the piston. 

The engine used for this experiment was an 11 J in. X 21 in. 
Crossley engine having a compression ratio of 6-37. The 
following is an extract from the report on the trial : — 

'The engine was run continuously for 120 hours on an 
electrical load with coal-gas. The engine developed during 
this period 43 B.H.P. on the average, and ran very 
smoothly and steadily. The average mean effective pressure 
was 101 lb. per sq. in. When jacketed, the engine would not 
develop more than 40 B.H.P. continuously without over- 
heating, and mixtures giving a mean pressure of more 
than 100 lb. per sq. in. produced excessive maximum pressures 
(over 300 lb.) with violent thumping explosions. The reduc- 
tion in maximum pressure, under these circumstances, by 
water-injection is over 100 lb. per sq. in., and the effect is 
very marked, the explosion becoming almost inaudible. This 
effect of the presence of steam in the explosive charge is, of 
course, well known, but the quantity of steam formed in an 
engine cooled in this manner is so large that it constitute- 



cha1\ v] THE GAS ENGINE 123 

substantial advantage of the method. It will be noticed that 
the formation of the steam does not involve any thermodynamic 
loss, such as occurs when water is sprayed into the cylinder 
in an atomised condition and evaporated before reaching the 
walls,, since the heat used is that which would otherwise be 
wasted in the jacket-water. The quantity of water used on 
this trial was, on the average, 102 lb. per hour, equivalent to 
2-4 lb. per B.H.P.-hour. The temperature of the engine 
varied from 150° to 180° C. No water was visible on the 
piston or the spindles of the valves, and when the engine 
was stopped at the end of the trial the inside of the 
combustion-chamber was found to be perfectly dry. When 
the engine was jacketed, and giving the same power for 
short periods, the jacket- water removed about 67,000 B.Th.U. 
per hour, which would be sufficient to evaporate 108 lb. of 
water at a temperature of 20° C. under atmospheric pres- 
sure. The agreement between the available heat and the 
amount of water evaporated is satisfactory, such difference 
as there is being accounted for partly by greater radiation loss, 
consequent on the higher temperature of the engine, and partly 
by the reduction in flame temperature produced by the 
steam, which somewhat reduces the total amount of heat 
passing into the walls. 

" The engine consumed in this trial 15 cub. ft. of Cambridge 
coal-gas per B.H.P. hour, reckoned at atmospheric tem- 
perature and pressure. This is approximately the same as 
it burnt when developing the same power for short periods 
when jacketed. Tests at other loads have shown that with a 
weak mixture the gas consumption is slightly increased by the 
water injection, but with very strong mixtures it is a trifle 
less. The difference, however, does not exceed 5 per cent, 
either way, and on the average it may be said that the economy 
is unaffected by the use of this method of cooling. Indicator 
diagrams taken in this long trial compared with similar dia- 
grams taken from the jacketed engine shows that the reduction 
in maximum pressure is counterbalanced by a slightly raised 
expansion line. The pressure is better sustained, partly by the 
formation of the steam and partly by the reduced loss of heat, 
with the result that the diagram is ' fatter ' and less ' peaky.' " 



124 THE INTERNAL COMBUSTION ENGINE [chap, v 

The method has since been successfully applied to much 
larger engines. 

86. The Super -Compression Method. — This method is due 
to Dugald Clerk, who in his James Forrest Lecture (1904) 
before the Institution of Civil Engineers, described it thus : 
;; Some time ago it appeared to me possible to reduce maximum 
temperatures by increasing the charge weight per stroke given 
to an engine. I had experimented with two engines, one 
having a 7 in. cylinder, 15 in. stroke, and the other a 10 in. 
cylinder. 18 in. stroke. These engines, which are of the 
ordinary standard four-cycle type, are allowed to take in 
the usual charge of gas and air ; then at the end of the stroke 
a further charge of air or other inert fluid is added to increase 
the pressure in the cylinder to 7 lb. or 8 lb. per square inch 
above atmosphere before the return of the piston. A small 
part of the return stroke is, however, made before the pressure 
can be materially increased as the added charge takes some 
time to fill the cylinder. This has the effect of increasing the 
charge weight present in the cylinder by about 40 per cent, 
and of increasing the pressure of compression without, however, 
increasing the temperature of compression. Indeed in both 
experiments the temperature of compression was diminished. 
As the charge present is constant so far as gas is concerned, 
the maximum temperature capable of being produced is much 
reduced. The maximum temperature shown by the diagrams 
taken by me from these two engines is about 1,200° C. Experi- 
ments were made and it was found that the heat-flow was 
reduced to about two-thirds, and further that the mean 
available pressure was increased about 20 per cent." 

The thermal efficiency of an engine which on working 

without super-compression was 27-7 per cent, showed an 

increase to 34-4 per cent, when super-compression was adopted. 

One sees therefore that if the atmospheric pressure were 50 per 

cent, higher than it is, it would suit the working of gas engines 

a great deal better.* 

* The converse of this is seen in the case of engines which have to 
work at stations which are at a considerable height above sea level. 
The horse-power under these conditions is stated to fall off by 3 per 
cent, for every 1,000 ft. of altitude, and this is the usual allowance 
made bv manufacturers. 



( hap. v| THE GAS ENGINK 125 

The improvements in operation obtained by the water 
injection and the super-compression methods are of course 
desirable in themselves, but they are really the most welcome 
for what they bring in their train, viz. freedom from cracking 
of cylinders and pistons. Whenever a large amount of heat 
has to be passed through the Avails to the cooling water (and 
the larger the engine the larger the amount of heat to be got 
rid of in this way and the smaller in proportion to cubic 
contents is the cooling surface), there arises a steep heat 
gradient in the metal in contact with the gas, which in turn 
leads to differential expansion and the consequent failure of 
engines owing to the cracking of ends or walls or sometimes of 
pistons themselves. Manufacturers who seek high thermal 
efficiencies seek them not so much for the resulting economy 
in fuel, but for the increased freedom from mechanical 
difficulties in operation. Improved methods which allow 
of the maximum cyclic temperature being reduced without 
any loss of power can also be pressed in the direction of 
increasing the mean pressure considerably without, however, 
raising the temperature so high as it was previously. This 
leads to greater output, but the pressure at exhaust is con- 
siderable, and it would in such cases be an advantage to use 
this exhaust in another cylinder and so compound the engine. 
Efforts in this direction have been made, but the difficulties 
of construction are great. 

87. The Indicator.- — A very important instrument used 
in connexion with gas engines is the indicator. It is an appar- 
atus which when attached to an engine draws a curve showing 
how the pressure in the cylinder varies at different points in 
the stroke. The best known modern form is the Crosby 
shown in Fig. 37. On the left of the illustration will be 
seen a small cylinder containing a cup-shaped piston which is 
regulated in its upward motion by the downward push of 
the strong spring seen above. When the indicator is screwed 
on to the engine cylinder the gas pressure causes the indicator 
piston to rise through a distance proportional to the force 
exerted. The little piston rod rises also and communicates 
its motion to the long sloping lever seen above. This lever 
carries at its far end a pencil which traces a line on a paper 



126 THE LXTERXAL COMBUSTION ENGINE [chap, v 

sheet fastened round the drum seen on the right which is 
made to oscillate to and fro by the cord shown on the extreme 
right of the diagram being attached to a moving link which has 
a motion similar to that of the piston, but less in amount. 
The pencil therefore traces out the closed curve known as 
indicator diagram. 

Fiff. 38 shows another form of the instrument ha vino- the 

: tside, where it is less affected by the heat and so gives 

a better reading. Of course all these springs need to be care- 





F::-. 37. — Crosby Indicator with 
Internal Spring. 



Fig. 38. — Crosby Indicator 
with External Spring. 



fully cahbra ted in advance so that it is known how much pres- 
sure is represented by a rise of the pencil point equal to. say. 
1 inch. There are certain qualities which a well-designed indi- 
cator should have. It must have a spring stiff enough to ensure 
that the maximum pressure will come well within its range. 
It must have a well-designed piston., as light as is consistent 
with strength, which will move freely in the cylinder. A 
slight leakage of gas is much less of an evil than any chance 
of the piston sticking or jambing. In the Crosby form the 
piston is made from a solid piece of tool steel, hardened and 
then ground, and lapped to gauge. It is provided with a 
- ket to receive the bead at the end of the spring and has 



OHAP. V | 



THE GAS ENGINE 



127 



screw adjustments for locking the spring in place. As has 
already been indicated, the to and fro motion of the 
paper is obtained from a cord attached at its other end to some 
point in the upper part of a swinging lever of which the lowest 
point is connected with the engine piston or some part that 
moves with it, so that the motion of the engine piston is 
reproduced to a convenient 
scale. There is also a 
Crosby reducing device for 
doing this. It is illustrated 
in Fig. 39, and its principle 
of action is easily seen 
therefrom. In this device 
the cord at the bottom can 
be fastened direct to the 
crosshead, or other part at- 
tached to the piston, the 
cord passing over guide pul- 
leys if necessary. It is 
better, however, not to have 
a longer cord than necessary, 
lest its stretching with the 
pull put on it should intro- 
duce error in the indicator 
card. For very accurate 
work the cord is some- 
times replaced by steel wire. 

88. Reflecting Types of Indicator.— Although the indicator 
is an important instrument in gas engine work, it does not 
occupy the position which it holds in steam engine practice 
where low T er speeds and pressures are met with. A much more 
rapidly moving instrument is needed in internal combustion 
engines, and such indicators tend to be fragile and are 
therefore little used except for special investigations. The 
usual form of such indicator makes use of a beam of light 
reflected from a vertical mirror which is caused to tilt as 
the gas pressure rises ; at the same time the frame in which 
the mirror is held is made to move angularly to and fro in 
time with the motion of the crosshead, thus producing by 




Fig. 39. — Reducing Gear for Crosby 
Indicator. 



128 THE INTERNAL COMBUSTION ENGINE [chap, v 

the combination of motion the familiar shape of the indicator 
card. The beam of light, unlike the. steel levers of the older 
form of indicator, has no weight, and therefore no inertia to 
make it lag behind its true position. 

Several models are now in use. but the principle of action 
is much the same in all. A diagram showing this principle 
is given in Fig. -40. It consists of a small cylinder containing 
a piston, just as in the Crosby indicator. The spring, however, 
is a small straight steel beam, held at the ends, as shown in 
the diagram (in some instruments the spring is in the form of 



Pivot 
Mirror 




— -<.- — 



Piston 
Bod 



Piston 



Indicator Car 
Oscillation 
Framework 
For Folio wing 
Cross head 
Motion 



Indicator 
Cylinder 




Beam or 



L 



yht 



Fig. 40. — Hopkinson Flashlight Piston Indicator. 



a diaphragm again-t which the gas pressure acts without the 
intervention of a piston). The pressure bends this spring 
upwards and so tilts the little mirror about a pivot. A beam of 
light is made to shine on the mirror, and the tilting of the 
latter deflects the path of the reflected beam through twice the 
angle through which the mirror is tilted. The reflected beam 
therefore moves through an angle which is directly propor- 
tional to the gas pressure. To give the beam a sideways 
motion equivalent to the stroke of the engine, the rocking 
lever is made to reciprocate the bracket carrying the spring 
beam and the mirror. The mirror therefore gets a partial 
rotation about a horizontal axis proportional to the pressure 
and a partial rotation about a vertical axis proportional to 



chap, v] THE GAS ENGINE 129 

the stroke. This being so, the beam of light on being reflected 
from the mirror draws a true indicator diagram on the screen, 
and owing to the speed at which the spot of light moves upon 
the screen, the diagram will appear as a continuous curve. 
For permanent record a photographic plate replaces the screen. 
In this way accurate indicator cards can be obtained even at 
the highest engine speeds. 

Professor Hopkinson claims that with his instrument the 
indicated horse-power can be measured with an error of less 
than 1 per cent., whereas in the older forms errors of 5 per cent, 
or more were common. 

89. Mean Effective Pressure. — From an indicator diagram 
it is easy to find the mean effective pressure acting on the piston, 
i.e., the average pressure in the working stroke less an allow- 
ance for the opposing pressures in the idle strokes. There are 
two methods of doing this :— 

(1) A mechanical method, by using the planimeter. 

(2) A method of approximate computation, by using what 

is called the " mid-ordinate rule." 

The planimeter is made to follow the pencil line continuously 
and so automatically to subtract the area due to the lower 
part of the diagram ; it thus measures directly the area in sq. 
inches of the closed figure ; if this area be divided by the 
horizontal length of the diagram in inches, it will give the 
average breadth of the figure measured vertically, and this, by 
using the scale of conversion for the indicator spring employed, 
gives the mean pressure in pounds per sq. inch.* 

In the second method a series of equidistant vertical lines 
(usually eleven in number) are drawn across the diagram as 
shown in Fig. 41, so that the first and the last just touch the 
two ends of the diagram. The mid-ordinates bisecting these 
spaces are then drawn (shown dotted in the figure) ; the 
lengths included within the diagram of these mid-ordinates are 
then measured and their sum divided by the number of them. 

* In the case of a four-stroke engine it might at first sight seem 
desirable to divide the average pressure over the two outward strokes 
and not on one of them only, but the accepted conventio n is that given 
in the text. 

K 



130 THE INTERNAL COMBUSTION ENGINE [chap, v 

This method gives, as before, the average breadth of the 
diagram measured parallel to the pressure axis, and so the 
mean effective pressure is obtained. 




Fig. 41.— Obtaining Area by Mid-ordinate Rule. Area C D E counts as 
positive ; area A B as negative. Mid-ordinate height of negative loop 
must be subtracted from that of positive loop. 

90. Effect of Engine Speed. — The Crosby indicator above 
described is well suited to gas engines running at normal 




Fig. 42. — Indicator Diagram taken from a fast running Engine with a Weak 
Indicator Spring. When expansion curve is wavy, the I.H.P. cannot 
safelv be determined from the diagram. 



speeds, but not to petrol engines, which sometimes run at 
2500 r.p.m. or even more, At speeds over 500 the effect 



(haf. v] THE GAS ENGINE 131 

of inertia-lag is felt even in the best of the pencil- indicators. 
At such speeds the piston has not time to get itself and the 
rods fastened to it into a position corresponding to that due 
to a steady pressure equal in amount to the momentary gas 
pressure, and the resulting diagram is therefore incorrect. 
Moreover, as the engine speed approaches the free-period of 
the moving parts of the indicator, the latter tends to vibrate 
sympathetically, and the lines drawn are wavy, as shown 
in Fig. 42. 

91. Estimating indicated from Brake Horse-Power. — Apart 
from difficulties with indicators at high speeds, it is far from 
easy to count accurately the number of explosions and to 
ensure that the " card " shows an average explosion. It is 
not unusual, therefore ; to measure I.H.P. by adding to the 
B.H.P. figure the B.H.P. necessary to rotate the engine light ; 
this assumes that the mechanical loss is constant at all loads. 
It is obvious that to assume that the friction at, say, the big 
and small ends of the connecting rod, or on the piston, will be 
the same whether there is any thrust in that rod or not, cannot 
be strictly accurate, but Professor Hopkinson has carried out a 
complete series of tests, using the reflecting type of indicator 
already mentioned, to elucidate this point. He found that 
" the difference between indicated horse-power and brake 
horse-power is rather less than the horse-power at no load 
under the same conditions of lubrication, mainly because of 
the difference in the power absorbed in pumping. In the par- 
ticular engine tested, the error from this cause in obtaining the 
indicated power would amount to about 5 per cent. The 
friction is substantially constant from no load to full load, 
provided that the temperature of the cylinder walls is kept the 
same, but the influence of temperature is very great." He 
found the mechanical losses in a 41 H.P. engine to be as 
follows : — 

Suction . . . . .3-4 per cent, of I.H.P. 

Piston friction . . . .6-1 ,, ,, 

Other friction (valve lifting, etc.) . 2-7 ,, ,, 

Total 12-2 



132 THE INTERNAL COMBUSTION ENGINE [chap, v 

92. Analysis of Motion of Indicator Piston. — It is important 
to examine mathematically the movement of an indicator 
when set to observe a very rapidly changing pressure. The 
piston used in the indicator instrument cannot be absolutely 
weightless whatever improvement may be made in reducing 
the weights of the moving levers (either by adopting lighter 
scantlings or by using a beam of light). Let the pressure 
acting on the base of the piston of mass M at any time to be p. 
also let piston area = a and the motion of the piston be S 
inches for each pound per sq. inch of pressure acting upon it. 
Then the forces acting on the piston when at a point x above 
its lowest position are : — 
upwards pXa 



x 
downwards — . a -f-M 



d 2 x 



S ' dt 2 

d x a 

therefore -^Tlj H ■ x= P- a - 

dt o 



or 



d 2 x 



ci pa 



dfi l m mX ~~W ' ' ' (1) 

Integrate this. The Particular Integral is 

1 pa SM 1 pa 



x- 



-I # SM pa ~ 

so that x= x — =p.S 

a M 

and the Complementary Function is 

a • / a . t, /a 

.r=Asm\/ . *+Bcos\/ . t 

v SM V SM 

So that the Complete Integral is 

x=Asin\/-^- . t +Bcos\/ — . t+p.S 
v SM ^ v SM ^ 

Now when t = o, x = o 

therefore B= — pS 

dx / a / 



. Acos\/ . t — Ba/ . sin\/ — 

v SM V SM V SM V SM 



chap, v I THE GAS ENGINE 133 

and when t=o, — =o 
dt 

therefore A=o 

Substitute these values of A and B and 

a?=wS->'l — cos\/ ,t\. This means that 

7 1 v SM J 

the piston rises to a height pS and then oscillates about that 

position with a frequency equal to — \/ — . 

All this assumes, however, that p is a constant or that it 
increases with such rapidity that it assumes its final value 
before the indicator piston has had time to move. It would 
have been more accurate to assume p to rise from zero to its 

final value in, say, — th part of a second and to consider what 

n 

happens during this interval. " To do this put p = a x .t where 

<*i has the constant value given by the equation : — final value 

oi pressure= — . 
n 

Equation (1) now becomes 

d 2 x , a a 

— jr-H 'x=—.a 1 t ... (2) 

and the Particular Integral 

SM/ , SM-^oN- 1 a ia 

a \ ^ a J M 

SM aa x . . 
t=oa 1 t. 



a M 
Therefore the Complete Integral would be 

x=A sin\ / — . tA-B cos\ / . 2+Scti*. 

v SM v SM ^ 

And since x=o when t=o 
therefore B=o 

A. (a/Jut / \Aj a /Li/ , /->i 

gain — =\/ — . Acos\/ — . 2-USai 

8 dt V SM V SM ^ 



134 TR£ INTERNAL COMBUSTION ENGINE [chap, v 
dx 



but when t= ; 


: — =© 
dt 


so that 


= \ . : , A ~^ 


.-. : _ :: 




This gives us 


? - 1 



- /SM / a 

= >-: :— \ — sin \ — . f 

Xow Sa^ is height to which piston would rise under the 
slow static pressure— call it A so that Sa t t = h T and let / be 
the frequency of the free vibration of the indicator piston. 

Tien 



f == — \/ « — OT ~>?rf= / \/ - — 



so that *^=h-^ sin V — - * 

=h — — - sin 2-srft 



:: 



=- - : ..-- -— - • ■ 3 



This means a fractional lag of as a maximum, but 

^ 2wft 

for any particular case it can be calculated thus. We may 

put / as 300, which about represents the use of an instrument 

of the Hopkinson type. 

Then 

1 \ 

z—h 1 — sin 18901 \ 

18901 J 

It will be useful to compute a few values for this for cases 
in which the value of t is much shorter than the periodic time 
of the instrument. When this is so sin lH90f can be written 
with sufficient accuracy as 



chap, vj 



THE GAS ENGINE 
(18900 s 



i35 



or 



(1890/)- 

r 



x=h\l— 1 + 

\2 



6 

(1890/) 2 ' 
\ .6 

6 
The relation between x and t in these early stages is therefore 
parabolic. The time / starts, so to speak, first, but x soon 
increases and gradually catches up. 




Line showing actual 
rise of Pressure . 



Line showing record made 
by undamped Indicator. 



I 
250 



Time in Seconds 



Fig. 43. — Diagram illustrating the way in which an undamped Indicator 
would follow a rapid explosion. Period of Indicator, ^ >n sec. 



136 THE INTERNAL COMBUSTION ENGINE [chap, v 



Thus for 



For 



= 



[ 



I 

- i 



= 



i 



.= -006 






for 



f— ■ 

10 



-- 



= ' 



but for this value of t our approximation no longer holds. I : 

i = L t A i . i the calculation should proceed thus 



— = 
h 



[ 



=1- 
=1 



1 



sin I ] 



I \ 

1 

ES9 



sinl 1 

r = : — ' 



~ 



: 



showing that the instrument is beginning to pick up. Evi- 
dently therefore it will not do to use an instrument for recording 
an explosion occurring in j^ — -- . unless its own frequency 
exceeds 30C 

The following table shows a serie- :: values and in Fig 1 
they are shown plotted. 



t 

- 




am 1988* 




i 


1 


• 

n 

-t-72 


! ' 

- 

-: 

0- 

o 


- 16 
—0-21 

013 




IS 

- 
1-1 

1-21 
Wi 

100 


QQO 

L 


- 
L 


lOOO 

L 
500 

L 
- 

- 
1 

[ 



chap, v] THE GAS ENGINE 137 

x 
Whenever / is a multiple of ^—^ the value of— will be TOO. 

ft 

The above curve does not of course take account of the frac- 
tional forces which prevent the indicator piston continuing to 
vibrate indefinitely. Students are recommended to work the 
problem out, introducing into equation (2) a term representing 
the frictional force. The result will be to multiply the oscilla- 
tory term by a factor of the type e~~ qt which, when the student 
has plotted the resulting curves, will show that the straight 
line is soon followed once the curve comes up to and crosses it. 
From the curve in Fig. 43 it is clear that for recording an explo- 
sion occurring in 1 q sec. this indicator with its g-J-Q period 
would be inadequate. The piston would scarcely have moved. 
For an explosion occupying ten times as long, i.e. jqVo sec -' 
the indicator would still be lagging a long way behind. For 
a g-£-Q sec. explosion the actual maximum pressure would be 
very fairly represented, but not the shape of the explosion 
wave. In fact for useful readings the instrument should not 
be used for any sharper explosion than ^-q sec. For an ordin- 
ary gas engine explosion occurring in^-^-Q sec. the instrument 
would be quite satisfactory. 

93. Engine Tests. — These are the tests applied when the 
engine has been constructed and built. They consist in the 
actual running of the engine as nearly as possible under work- 
ing conditions. The longest run is at full load, and it is cus- 
tomary afterwards to run for a time at half load and at no 
load. Sometimes it is specified that runs should be made at 
three-quarter load and one-quarter load, and occasionally over- 
load tests are made. It is almost impossible for one 
observer to do all that is necessary in such a test. The 
workshop custom is to measure — 

(1) The brake-horse-power. 

(2) The amount of fuel used per hour. 

(3) The quantity of cooling water used per hour. 

(4) The rise in temperature of cooling water between inlet 

and outlet. 

(5) The revolutions per minute. 

Sometimes the indicated horse-power is also measured, but 



138 THE INTERNAL COMBUSTION ENGINE [chap, v 

with high-speed engines this is not usual. Two observers can 
carry out the above tests. When tests are made not as a 
matter of workshop routine but as a matter of special research 
in workshop or college laboratory a very large number of addi- 
tional tests are carried out and many observers are needed. 

Indicated horse-power is deduced from the indicator dia- 
gram, obtained in the manner already described, and the 
record of the number of explosions per minute. The work 
done in ft. -lb. in a working stroke is 

Mean effective pressure in lb. per sq. inch X area of 
piston in sq. inches X length of stroke in feet. 
This, multiplied by the number of working strokes per minute 
and divided by 33,000, gives the I.H.P. This is, of course, 

the same as the formula — — - — - — * given in books on the 

33,000 & 

steam engine, but it must be observed that N must be taken 
as the number of working strokes per minute, not the number 
of revolutions per minute, i.e. in a four-cycle engine N cannot 
be more than half the number of r.p.m. and may be much less 
if the governor should be cutting out explosions. 

Brake horse-power is the power exerted at the crank-shaft 
and it is measured by applying a frictional load to the fly- 
wheel, as shown in Fig. 44. A test of this kind is often called 
a " bench test." A number of wooden blocks are fitted loosely 
to the rims of the flywheel and connected together by one or 
more ropes or by a canvas belt. A number of heavy weights 
are hung as atP x and a spring balance is placed at P 2 . The 
distance D is measured in feet. As the force due to the weights 
Px is greater than the force at P 2 there will be a force acting 
against the direction of the arrow of P x — P 2 . The work done 
therefore by the flywheel in one revolution in the direction of 
the arrow = force X distance moved 

^(P.-P^XTrD, 

and if there be N revolutions per minute the 

BHP _ (Pi-P 2 )X7rDxN 
33,000 

As this power is all being spent in friction it produces heat, 



CHAP. V | 



THE (J AS ENGINE 



:*o 



and in the larger engines the flywheel has to be cooled by a 
water spray. In the very biggest engines even this is not 
enough and a special water churning brake is used, or else the 
load is " taken up " electrically. In the latter case, the engine 
drives a dynamo and the electrical output of the dynamo is 
measured in kilowatts, when if the efficiency of the dynamo 
be known the B.H.P. can be deduced by turning the K.W. 



D. - - 



J 




^>oy> Shape of Wood Blocks. 

Fig. 44. — Arrangement for Brake Horse-Power Test. 



into H.P. and dividing the result by the dynamo efficiency. 

"D Tip 

94. Mechanical Efficiency. — The ratio of ' ' ' is the 

mechanical efficiency of the engine. It is usually from 75 per 
cent, to 85 per cent, at full load. The amount by which the 
I. H.P. exceeds the B.H.P. measures the power lost in engine 
friction. It is nearly independent of the load.* Thus in a 
special test of an engine of 76 I. H.P. the engine friction was 
found to be 

10-8 H.P. at no load 

11-0 H.P. at i load 

11-7 H.P. at full load 

in each case the r.p.m. being nearly 200. 

* See p. 131. 



140 THE INTERNAL COMBUSTION ENGINE [chap, v 

These figures show that engine friction is almost indepen- 
dent of the load. It rises however very rapidly with rise in 
speed. 

95. Measurement of Cooling Water. — From time to time 
during the test a measuring vessel can be placed under the 
outlet, or in some other convenient way a measurement be 
made of the number of gallons of water passing through the 
water jacket per hour. A thermometer is placed in the inlet 
and another in the outlet. Then the rise in temperature of the 
water multiplied by the number of pounds of water flowing per 
hour gives the number of heat units carried away by the 
cooling water per hour. 

96. Heat in Exhaust Gases. — The record of the test will 
show the amount of fuel used per hour. Its calorific value is 
either known in advance or is measured at the time. This 
gives the number of heat units supplied per hour. Some of 
these are turned into work (B.H.P.) ; others are lost in engine 
friction (I.H.P. minus B.H.P.) ; others are carried away in 
the cooling water ; and the residue are carried away in the hot 
exhaust gases. As it is not very easy to measure the quantity 
and temperature of the exhaust gases, it is customary to 
ascertain the amount of this loss by a subtraction sum. The 
B.H.P. expressed in heat units per minute is added to the heat 
units lost per minute in engine friction and to the cooling 
water loss per minute. Then this total is subtracted from the 
heat units supplied to the engine per minute, and the result is 
called the exhaust loss. 

The engine friction itself produces heat, some of which may 
find its way into the cooling water. Again, the exhaust gases 
in passing out of the cylinder often come into contact with a 
portion of the water jacket and give heat to the cooling water. 
Both tend to exaggerate the true cooling water loss, but their 
effect is not considerable. 

A suitable test report form for entering up these measure- 
ments is reproduced opposite. 

97. Heat Balance-sheets. — A heat balance-sheet as applied 
to a gas engine is a statement of the way in which the total 
amount of heat passed into the engine is employed. In the 



No. of engine 

Dia. of cylr 

Stroke 

Revs, per min 

Cyclic irregularity (when known) 

Rated B.H.P 

Area of producer grate 

Nature of vaporiser 

,, governor 



Gallons 
per min. 



(16) 



Quantity of water 
used in 



Producer. 



(17) 



Scrubber. 



Max. pressure 

from indicator 

card. 



(18) 



(19; 



Remarks. 

(State nature of load 
applied and of 

ignition 
arrangements. ) 



(20) 




Compression ratio 

" Air standard " of efficiency 

"D„4-;~ indicated thermal efficiency 

-Tvatio — — 

air standard erhciency 

Observer. 

Date 



Report No 

Fuel Consumption' Test. 



INTERNAL COMBUSTION ENGINE TEST REPORT. 
Maker of Engine , Maker of Producer . . . 

Nature of Fuel used during test Cat Value. . . 



No. of engine 

Dia. of cylr 

Stroke " 

Cyclic irregularity (when known) 

Rated B.H.P 

Area of producer grate 

Nature of vaporiser 

„ governor 



i init-t. 



(iOYRitXOi: TEST. 



Load on, steady speed 

Load off, momentary maxm, spee 

„ „ steady speed 
Load on, momentary min. speed 



Quantity .if fuel used. 



Cu. ft. of gas 
uppl.-id t<i L-tLKin. 
meter reading), 



(State nature of lot 
applied and of 

iwriuigements. ) 



HEAT ACCOUNT, 
(Full Load.) 
J Thermal equiv. of work done per 
J Loss due to engine friction „ 

Heat loss in jacket „ 

^ „ ,, ,, exhaust „ 

Heat received ,, 




CHAP. V] 



THE GAS ENGINE 



141 



early days of gas engine work it was easy to remember that 
roughly — 

Heat passed to water jacket . . 40 per cent. 

Heat left in exhaust gases . .40 ,, 

Heat converted into work . .20 



100 



In the experiments made by the Institution of Civil En- 
gineers' Committee the full-load heat balance-sheet was given 
as : 



Designation of Engine. 



Exhaust waste 
Jacket waste 
Radiation 
B.H.P. . . 

Total 



35-3 

23-5 

7-6 

26-7 



R. 



40-0 
29-3 
100 

28-3 



93-1 



107-6 



X. 



39-5 

250 

7-3 

29-8 



101-6 



In these experiments the exhaust waste was measured 
by passing the exhaust gases into a water-jet calorimeter'. 
Jacket waste was measured as the product of quantity of 
cooling water passed and rise of temperature. Radiation 
includes engine friction as well as radiation proper. B.H.P. 
was measured by a rope brake. 

Engine L shows a deficit in the total, so that there must 
have been some error in the experiments. Dugald Clerk 
in his paper * before the Institution of Civil Engineers, " On 
the Limits of Thermal Efficiency in Internal Combustion 
Motors," endeavoured to correct this measurement from 
several different possible points of view. He also extended 
the same treatment to tests R and X in order to get the true 
balance-sheet, and putting in I.H.P. instead of B.H.P. (the 
Committee's records were complete enough to permit of this), 
he found : — 

* February 26, 1907. 



142 THE INTERNAL COMBUSTION ENGINE [chap, v 



Designation 


of Engine. 


L. 


R. 


X. 


Exhaust waste . 
Jacket waste and 
I.H.P. . . . 


radiation . 


410 

27-2 
31-8 


371 
29-6 
33-3 


39-9 
25-4 
34-7 






Total 


100-0 


100-0 


1000 



Clerk then points out that the 27-2 per cent, of jacket 
waste and radiation for test L is obviously too low, and that 
heat appears to have been lost in some way. He therefore 
took the total of the exhaust waste and jacket waste and 
radiation items, i.e. 68-2 per cent, and attributed 34-1 per cent, 
to each, so making the balance sheet into : — 



Designation of Engine. 


L. 


R. 


X. 


Exhaust waste 

Jacket waste and radiation . 
I.H.P 


341 
341 

31-8 


371 
29-6 
33-3 


39-9 
25-4 
34-7 


Total 


1000 


100-0 


1000 



Clerk considered this balance-sheet probably represented 
the distribution of heat in the engines more accurately than 
either of the others. 

These various attempts at a heat balance-sheet have been 
given in order to show how very difficult it is to obtain a really 
accurate statement. The exhaust wastes originally given for 
L, R and X were 35-3 per cent., 40'0 per cent., and 39-5 per 
cent., and have now become 34*1 per cent., 37-1 per cent, and 
39-9 per cent. 

But the matter does not end even here, as Clerk brought 
into use the values found by him for the specific heat — values 
which showed a marked increase with rise of specific heat — 
and used them in some separate experiments of his own with 



CHAP. V] 



THE GAS ENGINE 



the engine X used by the Committee. He then found that 
the balance-sheet became : — 

Heat-flow during explosion and 

expansion . . . . .16-1 per cent. 

Heat contained in gases at end of 

expansion . . . .49-3 ,, 
I.H.P 34-6 



100-0 



Compare this with the balance-sheet given on p. 142 based 
on the Committee's experiments : — 





Committee's 
Trials. 


Mr. D. C's. 

Trials. 


Heat -flow during explosion and expansion . 
Heat contained in gases at end of expansion 
I.H.P 


25-4 
39-9 
34-7 


161 
49-3 
34-6 


Total 


1000 


1000 



The discrepancies shown here are indeed serious. 
Clerk's comment on them is as follows : " The indicated 
w r ork is practically the same in both trials and the sum of 
the other two items is the same also, but the distribution is 
different. Less heat flows through the cylinder- walls as 
determined by the author's (Mr. Clerk's) new method, and 
the exhaust gases contain more heat than the Committee's 
calorimeter trials show. The ordinary trials show 9-3 per 
cent, too much heat as passing through the cylinder- walls, and 
practically the same amount too little appears in the exhaust 
calorimeter. That is, 18-8 per cent, of the total heat remaining 
in the hot gases at the end of the expansion passes into the 
cylinder water-jacket during the flow through the exhaust 
valve upon the first opening and while the piston is making 
its exhaust stroke. This seems to be a quite reasonable 
portion of the total heat, such a portion as experience would 
lead one to expect. These new diagram trials afford, in the 



144 THE INTERNAL COMBUSTION ENGINE [chap, v 

author's (Mr. Clerk's) view, a more accurate heat- distribution 
balance-sheet than has yet been obtained in any engine, from 
which can be deduced the ideal efficiency of the working fluid. 
Adding together 

Heat contained in gases at end of expansion . 49-3 
I.H.P 34-6 

83-9 

34-6 

Then = 0-41^ That is, if this balance-sheet be correct 

83-9 

and the heat loss be assumed as entirely incurred at the begin- 
ning of the stroke, then the maximum efficiency of the actual 
working fluid for the compression and expansion is 41 per cent.* 
of the total heat supplied." 

Even with such very considerable discrepancies in the 
heat balance-sheets as those discussed above, the student 
will none the less remark that the heat utilized has now grown 
from about 20 per cent, to well over 30 per cent. This 
all-important improvement has occurred therefore in spite 
of the many uncertainties as to how the lost heat divided 
itself up. It is indeed one of the fortunate features of gas 
engine manufacture that improvements do not have to attend 
the settlement of the many intricate problems with which gas 
engine operation is bound up, but proceed by the trial and 
error of experiment with such guidance as theoretical considera- 
tions have been able to afford. The great want which in the 
past caused so much theoretical difficulty was accurate know- 
ledge of the values of the specific heats of the working fluids. 

98. Engine Tests. — (a) The following figures are taken from 
a test on a 200 H.P. engine and suction plant by Mathot.f 
The engine was of the four-cycle double-acting type and was 
tested at the works of the well-known firm of Gasmotoren 
Fabrik, Deutz-Cologne. 

Piston diam. . . . . . 21 J in. 

„ stroke ..... 27 T 9 g- in. 

* The "Air standard" efficiency for this engine = 049; the "Gas 
standard" of efficiency would (see p. 85) be 81 per cent, of this or 
0*40, which is very near the figure above given. f I.M.E., 1905. 






CHAP. V] 



THE GAS ENGINE 

Full Load Tests. 



145 



1904. 



Average r.p.m 

B.H.P 

Duration of test, hours 

Average temperature of water after cool- 
ing piston 

Average temperature of water after cool- 
ing cylinder and valve seats 

Water consumption for cooling piston, 
gallons /hour 

Water consumption per hour in vaporizer 
(anthracite fuel), galls, /hour 

Water consumption per hour in scrub- 
bers, galls, /hour 

Average temperature of gas at outlet of 
generator -. 

Average temperature of gas at outlet of 
scrubbers 

Gross fuel consumption per B.H.P. hour 

Corresponding Thermal efficiency 



March 14. 


March 15. 


151-29 

214-22 

3 


150-20 

222-83 

10 


117-5° F. 


— ■ 


135° F. 


— 


39 


— 


■ — 


14-2 


— 


318 


— 


558° F. 


0-727 lb.* 
19 per C3nt. 


62-5° F. 

0720 lb. 

24-4 per cent. 



Other interesting figures are — 

Water consumption in galls, per B.H.P. -hour — 

1. For cooling cylinder, stuffing boxes, valve 

seats and jackets . . . . .4-65 

2. For cooling piston and piston rods . . 1-75 

3. For vaporizer ...... 0-0655 

4. For washing the gas in the scrubbers. . 1-42 
Also : — 

Water converted into steam 
per lb. of fuel consumed in 
generator . . . .0-193 galls, or 1-93 lb. 

(b) In a careful test carried out by J. T. Nicolson on a 
Crossley gas engine and suction producer plant, the calorific 
value of the gas was 156-5 B.Th.U. as determined by analysis, 
and 149 B.Th.U. per cubic foot by Junker's calorimeter at 

* Includes fourteen hours of fires banked up. 



146 THE INTERNAL COMBUSTION ENGINE [chap, v 



the temperature and pressure of the calorimeter. The following 
measurements were made : — 

B.H.P. = 559. 

Gas per hour = 29,037 cu. ft. corrected to 0° C. and 760 mm. 

Gas per B.H.P. = 51-94 cu. ft. 

Heat supplied = 51-94 X 156-5 = 8,128 B.Th.U. per B.H.P.- 

, ,, , ,, . „ 1.980,000 1 2,546 
hour Brake thermal efficiency^— X =— = 

J 778 8,128 8,128 

31-3 per cent. 

Variation in engine speed when horse-power was instan- 
taneously dropped from 600 to 50 was from 11 9-4 to 121-4r. p.m., 
corresponding to a total variation of 1|- per cent, of mean 
speed. No back-firing was observed to take place when 
this was done. These tests show remarkably good thermal 
efficiency and satisfactory closeness of governing. 

(c) A third trial is that of a 150 B.H.P. six cylinder vertical 
gas engine which w r as run for six hours on full load. The 
gas was taken from a pressure producer and had its calorific' 
value measured every hour by a Simmance-Abady Calori- 
meter. Readings were taken every half -hour of the B.H.P. 



Average air temperature . 

Average air pressure 

Cu. ft. gas used per hour 

Average Calorific value (lower) 

Engine speed . 

B.H.P. 



72-2° F. 

29-56" Hg. 

13,000. 

128-1 B.Th.U. per cu. ft. 

325 r.p.m. 

151-3. 



B.Th.U. consumed by engine per B.H.P.-hour = 10,590, show- 
ing a brake thermal efficiency of = 24-1 per cent. 

& J 10,590X778 r 

99. Governors. — The most usual type of governor has two 
balls fastened by arms to the shaft and rotating with it. Such 
governors are shown in Eigs. 45 and 46. In the former figure 
it is arranged on a vertical shaft, and in the second on a horizon- 
tal one. In Fig. 45 A is the shaft ; it carries on it the bracket 
CxCa, and at Q 1 and C 2 are hinged the arms T> x and D 2 carrying 
the balls B x and B 2 . As the shaft rotates the balls tend to 
fly outwards by centrifugal force, and in doing so lift the 






CHAP. V| 



THE GAS ENGINE 



147 




Fig. 45. — Vertical Governor. 



sliding collar F. To this collar can be attached a lever or a 

system of levers to act on the engine. The way in which they 

act will be discussed later. In Fig. 46 the same sort of action 

occurs. As the balls 

B x and B 2 fly out they 

carry with them the 

links Hi and H 2 which 

are hinged at C x and 

C 2 to the arms of a 

bracket G fixed on the 

shaft. This outward 

movement causes the 

sliding collar F to slide 

towards the fixed collar 

D, and so to compress 

the spring E. The 

faster the shaft A 

rotates the more the 

spring is compressed. 

In the vertical governor the effort of the balls to fly out is 

balanced against gravity. In the horizontal form it is 

balanced against the force exerted by the spring. The hori- 
zontal governor is 
most used with in- 
ternal combustion en- 
gines. 

100. Method of 
Controlling Engine. — 
The motion of the 
sliding sleeve of 
either the horizontal 
or vertical governor 
causes a lever to be 
moved which controls 
the engine and brings 
it back to its correct 

speed. This lever can be used to — 

(1) Cut off the whole of the fuel supply for one or more 
strokes ; or 




Fig. 46. — Horizontal Governor. 



14S THE INTERNAL COMBUSTION ENGINE [chap, v 



(2) Reduce the amount of fuel used per cycle, leaving the air 

supply untouched ; or 

(3) Reduce the amount of both fuel and air keeping the pro- 

portion of fuel to air the same ; or 

(4) Cause the ignition to come later, or be cut off altogether. 

101. Hit and Miss Governing. — The first of these alterna- 
tives is known as *'*' hit-and-miss " governing, because when 
the speed gets too high the governor lever is made to lift up a 
small piece of metal which lies between the gas valve tappet 
and the valve stem. This is shown in Fig. 47. B is the piece 
of metal in question. When the cam E pushes the roller G 

it makes the tappet rod 
GDC. which is pivoted at 
D. push the valve A open. 
(The valve A is the gas 
admission valve ; after 
the gas passes this valve 
it joins the air supply, 
and both pass through a 
larger valve, which opens 
a little earlier, into the 
cvlinder. ) This could not 
be done if B were not in 
line between C and A as 
shown. The governor 
lever lifts B out of this 
line when the speed is too 
high, and the valve A is 
consequently not opened and no gas reaches the cylinder. 
This reduces the engine speed until the governor again inserts 
the piece B. The engine speed will therefore be kept steady 
at all loads up to the maximum load the engine can take. 

The effect of hit and miss governing is clearly shown on 
the indicator diagram. In Fig. 48 is shown such a diagram 
taken during two successive strokes of an engine. The " hit " 
or working stroke is shown at ACD. and the " miss " or idle 
stroke is shown at AB. The compression line of " miss " 
stroke lies below that of the " hit." This is because the gas 
valve is closed on the suction stroke and the air valve acting 




Fig. 47. — Diagram illustrating a Hit- 
and-Miss " Mechanism. 



chap, v] THE GAS ENGINE 140 

alone is not large enough to fill the cylinder without throttling 
the entering air, with the consequence that the " miss " suction 
pressure line lies below that of the " hit " suction. It will 
be noticed, moreover that the compression line AB almost coin- 
cides with the expansion line BA. In order to exhibit better 
what was going on during the two suction strokes a " suction : ' 
diagram was taken. It is shown in Fig. 49. A suction diagram 
is one taken with a very weak spring and with a stop fixed 
above the indicator piston to limit its rising above a point 
corresponding to about 3 lb. persq. inch. The " hit " and the 
" miss " suction strokes both start at A, but the latter lies 
at AB much below the former at AD. The beginning of the 
compression strokes are respectively BC and DE. FA is the 
exhaust line after explosion, and it is seen to fall below the 




Fig. 48. — Indicator Diagram, from a 25 h.p. gas engine, showing effect of 

" Hit and -Miss " Governing. 

atmospheric line ; this shows the very useful " scavenging," or 
clearing out, effect of the rush of exhaust gases along the 
exhaust pipe. 

102. Exhaust Governing. — The second of the alternatives 
mentioned in paragraph 100 is called quality governing, as the 
governor is here used to reduce the working charge in richness 
or quality. It does this by partly cutting off the fuel supply. 
This reduces the mean thermal value of the charge admitted, 
with the result that the pressure produced is less and the engine 
speed falls to its normal value. The disadvantage of this 
method of governing is that the composition of the mixture is 
continually varying, and it is not possible to find any fixed 
ignition point to suit all mixtures. Moreover if the mixture be 
made too weak it will not fire at all. 



150 THE INTERNAL COMBUSTION ENGINE [chap. V 

103. Quantity Governing. — This is the method of the third 
of the alternatives given in paragraph 100. It consists in 
throttling the working charge, of air and gas, as it is about to 
enter the cylinder. The consequence is that at the end of the 
suction stroke only a part of the usual charge has got into the 
cylinder and the pressure is therefore less than atmospheric 
and the compression pressure is much reduced. The low 
compression pressure means a low explosion pressure and the 
engine speed therefore falls back to its normal amount. In 
this method of governing, as in those previously mentioned, 



Stop\ £/ci;aust 
, 3 



3 ib. in.- 



"w"~ 



C E 




Com press 'or. 
(air onlj) 

Compression 
'fgas i a'rj 



\D 



Suction 
[gas & &ir.j 







^7' 

Atmospheric . 
line . . 



u ct'i on 
(oLir only J 



Fig. 49. — " Suction " Diagram from same engine as Fig. 48. 



the compression ratio is unaffected, and the " air standard " 
of efficiency is also unaltered. Quantity governing is coming 
more into force. At one time it was only used on Continental 
engines, but now is very general in large engines made in 
England and America. 

104. Retarding Ignition. — This means of altering engine 
speed, though theoretically feasible, is not practical. To make 
the spark come later in the expansion stroke, instead of at the 
very beginning of it. is. of course, to diminish the average work- 
ing pressure and therefore the speed of the engine. But as it 
leads to the use of just as much fuel whether the engine is 
giving a full power stroke or not. it is uneconomical, and as 
moreover there is the risk of some of the charge getting into 
the exhaust unburnt it may lead to unpleasant explosions in 
the exhaust pipe. Chitting off the ignition altogether intro- 
duces the same disadvantages in an aggravated form. 

105. Present Practice. — Generally speaking large gas engines 
usually have quantity governing, whilst small ones very com- 



CHAP, v] THE GAS ENGINE 151 

monly have " hit-and-miss." Motor-car engines are usually 
governed by hand on the throttle, so producing an irregular 
sort of quantity governing. An objection to the " hit-and- 
miss " system is that in order to produce a reasonable mea- 
sure of uniformity of angular velocity in the crank shaft a 
very heavy flywheel becomes necessary. This adds to the 
cost of the engine and diminishes its mechanical efficiency. 
It may in fact be said that the two merits which have enabled 
the " hit-and-miss " gear to be used as much as it is, are its 
great mechanical simplicity and its ability to keep constant 
the proportions of gas and air in the incoming charge, so 
enabling the engine always to be run on its most economical 
mixture. Continental makers were the first to break away 
from this system of governing, by arranging that the governor 
should produce a variable lift of the gas valve by means of 
a conical cam. As the air supply was not interfered with 
this meant a continually changing richness of charge and 
hence a corresponding change in thermal efficiency ; this is 
well shown in Fig. 26 on p. 87. The tendency now is towards 
a regulation of both the gas and the air supplies by throttling 
them after mixture, with the advantage that the mixture 
being of constant composition the rate of ignition does not 
vary with the varying position of the governor. Present 
practice has not settled down to any definitely accepted 
standard, and there are few matters relating to the gas 
engine which are the subject of more patents. 

106. Turning Moment at Crank-Shaft. — The pressure exerted 
on the piston during the explosion stroke falls rapidly as the 
gases expand. Thus the total force exerted on the piston is far 
greater at the early part of the stroke than it is at mid-stroke 
and still greater than it is near the end of the stroke. Also 
the angle between the engine centre line and the connecting 
rod is continually changing ; as is the perpendicular distance 
from the crank-shaft centre to the line of the connecting rod. 
This leads to a very irregular turning effort at the crank- 
shaft. 

Thus in Fig. 50, if F be the force on the piston, P the force 
actingalong the rod, and R the reaction from the cylinder wall, 
R and P can be calculated when F is known by applying the 



152 THE INTERNAL COMBUSTION ENGINE [chap, v 



triangle of forces as shown ; thus P = F cosec BCA. The 
turning moment about the crank-shaft centre A 

= P. AB. sin ABC = F.AC. 
This is the torque that causes the engine to do work. 




Fig. 50. — Forces acting at Gudgeon Pin and at Crank Pin. 

In order to study it more fully it is necessary to consider 
the variation of F during the cycle. Now F is proportional- 
to the height of the indicator diagram, and if the four suc- 
cessive strokes of a four-stroke engine are set out in one straight 




(Exhaust) 



Suction 



Comoressiok Exp losion 



Exhaust 



(Suction) 



Fig. 51. — Effort tending to Rotate Crank in each of the Four Strokes. (Pres- 
sures opposing motion of crank-pin are shown as negative.) For indi- 
cated diagram represented, see Fig. 41. 

line and the indicator diagram lines are carefully reproduced, 
a diagram of the form shown in Fig. 51 is obtained. Care 
must be taken to allow for the sign of the pressure, e.g., in the 



CHAP. V] 



THE GAS ENGINE 



153 



portion of the curve corresponding to compression, the piston 
is retarding the motion of the crank-pin and F is negative ; 
that portion of the curve is therefore placed below the line AB 
in Fig. 51. The diagram repeats itself after every four 
strokes. It is obvious from Fig. 51 that the force F acting 
on the piston varies very greatly during the complete cycle. 
To remedy this it is possible to have two cylinders acting on 
the same crank-shaft and to put the cranks at an angle 
of 180° to one another. This means that while the first 
engine is on its explosion stroke the second will be on either 
its exhaust or compression strokes, so that the crank-shaft 
will get two impulses every four strokes instead of only one 
impulse. This may be further improved by having four 




180' 360° 540° 720' 

Fig. 52. — Same as Fig. 51, but with Four Cylinders. (Cranks at 180°.) 



cylinders so that there is an explosion in every half revolution 
and the net value of F is as shown in Fig. 52. Even this curve 
is very saw-toothed, but it gives a steadier forward effort on 
the crank-pin than does Fig. 51. 

107. Inertia Forces. — The curve of Fig. 52 is also subject 
to a further influence due to the inertia of the moving parts. 
If the engine rotated very slowly this correction would be of 
little importance, but at ordinary engine speeds it has consider- 
able influence. At the beginning of the explosion stroke the 
piston is at rest, and by mid-stroke it may be moving at 2000 



154 THE INTERNAL COMBUSTION ENGINE [chap, v 



ft. per min. This means a considerable acceleration and 
therefore calls for an equally considerable force to bring it 
about. Some of F, therefore, is required in overcoming the 
inertia of the piston and small end of the connecting rod before 
any force can be transmitted to the crank-pin. This force 
is not lost, but reappears as the piston slows down in the second 
half of the stroke. The effect of inertia is therefore to lower 
the peaks of Fig. 52 to an amount depending on the engine 
speed and to raise the valleys by a similar amount. This is 
a useful effect, as it tends to minimise the saw-toothedness and 



ISO' 



360 



>40' 



720' 



Fig. 53. — Same as Fig. 52, but with allowance for Inertia of 
Reciprocating Parts. 

change it into a curve similar to that in Fig. 53. The amount 
of this change depends on the speed of rotation, and varies in 
proportion to its square. 

108. Flywheel Effect. — The kinetic energy stored up in a 
flywheel is calculated from the following formula or one 
derived from it. 

KE.=iIco 2 ft.-lb. 

where I — moment of inertia about the axis of revolution 
and co = angular velocity in radians per second. 
From this it follows that 



d 

dco 



(KE) = Ico. 



For a small variation in co compared with KE it is therefore 
necessary that either I or oj should be large. For the ordinary 
purposes of industry it is sufficient to ensure that the range 



Chap, v | THE GAS ENGINE 155 

of angular velocity never exceeds by more than J 5 th to g^th 
part the mean speed. For the driving of continuous current 
generators only half the above variations are permissible, 
whilst for the driving of alternators in parallel the requirements 
are far more stringent, involving a permissible speed varia- 
tion of but j I th or even in some cases tj, 1 ) () th part of the mean. 
Mat hot * has suggested the following formula for use in cal- 
culating the dimensions which should be given to flywheels 
of different types of Otto cycle engines : — 



Tfi.a.ri 6 

where 

P = weight of rim (without arms or boss), in tons. 

D = diameter to centre of gravity of rim, in feet. 
a — degree of cyclic irregularity permissible. 

n == revolutions per minute. 

N = B.H.P. 

k = coefficient determined as below. 
For single cylinder, single acting . . . k = 475,000 

For two opposed cylinders, single acting, or one 

cylinder double acting . . . . k = 300,000 

For two cylinders, single acting, tandem or 

twin . . . . . . . k = 225,000 

For two cylinders, double acting, tandem or twin k = 75,000 

Note. — Total weight of flywheel may be put as 1*4 P. 

109. The usual way to speak of cyclic irregularity is that 
above described. t It amounts to defining cyclic irregu- 
larity as the fraction which the range of instantaneous 
angular velocity bears to its mean value in any one com- 
plete cycle. There is, however, another way of considering 
the matter. Thus Mr. L. Schiiler in a paper dealing with the 
driving by gas engines of alternators operated in parallel 
remarks : " The speed of the machines should be as uniform 

* Internal Combustion Engines (1910). 

| This is a more accapted way than that described in the first 
edition of this book. 



156 THE INTERNAL COMBUSTION ENGINE [chap, v 

as possible and should in any case be such that the amplitude 
of the angular oscillation does not exceed two electrical de- 
grees." An electric degree means of course 3-g^th part of the 
angular distance, the passage of which by the armature corre- 
ponds to one electrical cycle. It becomes therefore a matter 
of interest to see how the one form of computation can be 
turned into the other. A good deal depends naturally on the 
rate at which the speed variation rises and falls, but for a suffi- 
ciently close appro xim ation it may be taken as a sine or cosine 
curve. Then the angular velocity w may be written as equal 
to 

a — b cos cb. 

Where b is the angle the crank has moved through, a is the 
mean value of the angular velocity, and b is its maximum 
variation from the mean, so that the speed oscillates between 
(a -j- b) and [a — b). If c be unity this oscillation occurs once 
in a revolution, but if c = 2 then it occurs twice, and so 
on. 

This may be written 

m=—=a-\ J b cos cfl 
di 

or dt- 



a — b cos cb 



integrate and 



, cd 

\ a — b tan— 

ct=A— — ^=tan -1 

\ a 2 — b 2 A a+b 

where A is some constant. 

Put 6 = <:> when ( = and therefore A = 

. cd 

q V a — b tan _ 

so that t= — tan" 1 '' ■ ■ ■ ( 2 ) 

cVa*—b? \V/+6 

Xow _ is half the cvclic irregularity and may be given a 
a 

symbol — call it m. 



CHAP, v] THE GAS ENGINE 157 

7 cQ 

2 VI — m tan 9 

therefore t= , . tan -1 — — 

acVl—m 2 Vl+ra 

Vl-m tan- actVl^? 

— = tan 



Vl + 



m 



(2) 



2 _,(Vl+m aclVl—m 2 \ 
or . 0=— tan 1 ' — tan- -jr- -J 

c wi — m * 

Now as m is always small compared to unity Vl -f- m may 
be written as (1 + Jm) and m 2 be neglected ; 

therefore 0=1_ tan" 1 ! ( 1 +m)tan— J . 

Now were m really zero this equation would give to 6 a value 
equal to 

2 . _i , aci 
= — tan A tan — =at. 

c 2 

Call this value 6 . Really it means the position of the 
crank at the instant determined by t if the angular velocity 
were strictly uniform and equal to a. 

We may therefore write 6= — tan -1 l(l+ra) tan— | (3) 

which is the solution. 

If, for example, c=l and m= 

200 

then 6=2 tan -1 j 1-005 tan— 1. 

From this we see that when 6 = 120°, 6 becomes 

2 tan" 1 ! 1-005 tan 60°} 
= 2 tan" 1 (1-005 X 1-73205) 
= 2 tan" 1 1-74071 
= 2 X 60-12° 
= 120-24° 

or that the crank would be nearly J degree ahead of its 
supposed position. 



158 THE INTERNAL COMBUSTION ENGINE [chap, v 

It is useful to get an expression for this deviation directly. 
From 3 

0— 9 =— tan-ijfl-fm) tan-|- } — <V 

Find the inaxiniuni value of 6 — b - by differentiating and 

equating to zero. Then 

1 — m =. 1 — 1 — m -tan- — - cofi^— - 

2 ' 2 

= eos- — — (1 — >/> -sin- — 
2 2 

1=2 sm- — -\-m sm- — 
o o 

• ^o 1 

sm- — = 



-//? 



tan- — =- 



2 1 —in 



cO 

or tan " " — 1 — \m approximately. 

so that the maximum value of b — 6 is found from the 
expressions 

0— o =— tan-^l— Jm)(l+i»)— d 9 

c 

and 

O = — tair^l— |m). 

c 

Therefore the maximum deviation 

— J"_; t an -1 (l— Jr/m— tan -1 ( 1— lira) I 
c " " j 



o 



C 



-tan 



— l 



4w 



S— w> 2 



If ?/' be so small that irr ean be neglected — as it practically 
u — this reduces to 

Q m 

maximum deviation = — tan _: — . . . (4) 

c 2 






chap, v] THE GAS ENGINE 159 

If for example c = 1 and m = — , this equation gives the 
maximum deviation 

= 2 tan -1 — =2Xl*2=2-4 degrees. 

When m is much smaller than — , say equation (4) can 

be approximately written : — 

2 m m „ ,. i . . _ 1 

- X — = — • ho that with c=l and rn = - the maxi- 

c 2 c 200 

mum deviation would be radian or 0-28 degree. 

200 & 

Equation (2) shows how the value of 6 can be calculated 
for any position of the ideal crank, and the deviation may have 
its most important effect electrically even when it has not 
itself its largest numerical value. For that reason it is desir- 
able to have some means of calculating it easily. In cases in 
which it is only desired to find the maximum deviation to 
some approximate degree of accuracy, it is sufficient to take a 
mean value of the excess angular velocity and multiply it by 
the time during which it operates. Thus if as before c = 1 

and m= — , calling the angular velocity co, the average 

excess of angular velocity 

2 co co 

~ V 200 ~~ ToOtt 



7T 



and this operates through 180° or for a time equal to , so 



OJ 



that the angular motion gained 



co it 1 

X — = 



100tt co 100 

and radian = 0-57 deg. This, divided between the two 

100 6 

ends of the period, gives a maximum deviation of 0-28 deg., 

which agrees with the 0-28 deg. previously found. 



160 THE INTERNAL COMBUSTION ENGINE Yttat v 

Eoi these values of c and m it may be said that the maxi- 
mum deviation is about J :: a degree. If the alternator has 
six pairs of poles giving six electrical cycle* luring one mechani- 
cal one this deviation could also be called | 6 or one and a 
half electrical degrees, which corresponds with Mr. Schuler's 
result. 

110. Balancing.- — Th "Jem of balancing the parts of a 

_ - engine and providing for irniforrnity of torque as far as 
[ "—:':.- loes not differ in principle from the <: ending 

problem in the : ase of the steam engine, and the author does 
not prof jee therefore to devote a great deal of space to this 
subject. The student should refer to what has been written 
on the subject of balancing by Pi fessoi I erry and Profess 
Dalby. both of whom have made a special study of the matter. 
I: will, however, be advisable to give here a brief account of 
the general principles involved, leaving the application to be 
made fcc each and every problem as it presents itself. For 
it must be remembered that although the problem is often sur- 
rounded by complications which lead to the mathematical 
work looking difficult and involved, these > really no special 
difficulty about it at all. but merely a necessity that the funda- 
mental principles should be rightly applied and that the alge- 
braic or arithmetical work should be carried through without 
mistakes 

The simplest kind of balancing is that in which a flywheel 
is light on one side and requires a weight (Wi fastened to the 
other side in order to prevent any jumping or vibration when 
the wheel rotates. This does not of necessity mean that an 
equal weight must be added to the other side, because it does 
not follow that it will I e v : ssil le t j place the balance weight 
at the ss me instance from the :t::~:t : : the shaft, and the cen- 

trifugal force being equal be - — where cj= angular ve.:- 

9 
city in radians per — >nd and r = distance in feet from the 

..tie of the shaft ) it is evident that the product of the W and 

the r in the balance weight must me : at to a certain amount. 

If therefore the is very small then W must be i tionately 

_ eater, and inasmuch as the balance weight is often bolted in 

between the spokes it is clear that r will usually be less than 



chap, v] THE GAS ENGINE 161 

the radius of the rim of the wheel. This is the simplest kind 
of balancing. The most complicated kind occurs in the motion 
of a rod. like a connecting-rod, in which one end reciprocates 
to and fro in a straight line and the other end follows a circular 
path, with the result that intermediate parts of the rod follow 
a complicated curve and one not easy to treat. In such a case 
as this it is customary to obtain an approximate solution by 
assuming that a certain part of the rod is massed at the cross- 
head and the rest at the crank-pin, and it is not unusual to 
make this division of the rod in inverse proportion to the dis- 
tance of the centre of gravity from either end. This is only 
an approximation, unless it happens that the rod is so made 
(which it usually is not) that if hung up from the big and little 
ends in turn it will swing, pendulum wise, with the same number 
of swing-swangs per minute. When a number of rotating 
masses (real or assumed) have to be balanced it is useful, 
following Dalby's method, to consider the plane perpendicular 
to the shaft in which one or more of them lie to be rotating at 
the same speed as the shaft and to draw out on this plane the 
force diagram. 

111. The connecting rod influences the problem of the run- 
ning of the engine in another way. If the crank-pin rotated 
uniformly and the connecting rod were infinitely long the 
motion of the piston would be Simple Harmonic, and the dis- 
placement of the piston from the middle of its stroke would be 
r cos 6 at the instant when the angle between the crank and 
the line of dead centres was 6, the radius of the crank-pin 
circle being r. But the connecting rod in actual engines is 
usually quite short, never more than ten times the length of 
the crank arm, and usually much less. This produces a com- 
plicated motion of the piston, and it will be useful to calculate 
exactly what it is. Let P be the crank-pin and A the piston 
which, in the position shown, is at a distance AB from the 
beginning of its stroke. The angles 6 and cp are as shown in 
the diagram. OP is r and AP, I. AB will be written as x. 
Now it is clear that 

r cos 6 -f- 1 cos cp -f- x — BO 
and BO = l+r 

so that r ocs 6 -f- 1 cos cp -f- x = I -j- r . . . . (1) 

M 



162 THE INTERNAL COMBUSTION ENGINE [chap, v 

Also we have r sin 6 = 1 sin cp (2) 

It is necessary to combine these two equations so as to find 
x in terms of known quantities. 



i 



Fig. 54. — Motion of Crank-pin and Connecting Rod. 

From (1) 

x = I -\- r — r cos 6 — I cos cp 
= I (1 — cos cp) -\-r (1 — cos 0) 

Also from (2) 

T 

sin cp= — sin 6 



y — 



(3) 



and cos<p=V 1 — -^-sin 2 

V 

therefore x= l(l — V 1 — -^sin 2 ^ )-\-r(l — cos 6) . . 

and this gives the value of x for any value of 6. 

Previously we have spoken of the distance of the piston 
from the mid point of its stroke rather than from either end, 
and it is useful to follow the same procedure here — call the 
displacement of the piston from mid stroke y — then x -\- y = r 
or y=r — x 

so that y=r cos 6 — ill — V 1 — -~ sin 2 ) 

furthermore 6 is a function of the time, and since uniformity of 
rotation is assumed it will be directly proportional to the time. 
Put therefore 6 = cot 



so that y=r cos ojt — l(l — V 1 — — sin 2 cotj , , . (4) 



chap, v] THE GAS ENGINE 163 

Since, however ( — ) is a small amount in all engines an 
approximation to the above may be written as 

y=r cos cot — 1 1 1 — I -\-\—^sin 2 cot j 



i ■ u 



=r cos cot — — sin 2 cot 
21 

or y=r cos cot — — (1 — cos 2cot) ... (5) 

U 

This very interesting result shows that the position of the 
piston can be stated as the sum of two S.HJYL's one of which 
corresponds to an infinitely long connecting rod and the other 
to a S.H.M. of twice the periodicity and of an amplitude de- 
pending on the ratio of r to I. The motion in fact is analogous 
to that of the air set into vibration by an organ pipe which in 
addition to giving its fundamental note gives also a weak first 
harmonic. Although this first harmonic is weak in its effect 
on the displacement of the piston, it is considerably more potent 
when velocities and accelerations have to be taken into account, 
as will presently appear. 



Since from (5) 



/y£ 



y=zr cos cot — — (1 — cos 2col) 

dy . r 2 co . _ J 

— ~= — cor sin cot — sin 2 cot 

dt 21 

= — cor fsin cot -|— - sin 2 cot) ... (6) 
and l=— oPr (cos co*+— cos 2 co t\ ... (7) 

It is important to note that expression (6) which gives the 

r 
velocity of the piston at any point has the multiplier - in 

front of the harmonic term, and that expression (7) which 

gives the acceleration and therefore measures all the inertia 

r 
forces has the multiplier — . It follows therefore that the 

l 



164 THE INTERNAL COMBUSTION ENGINE [chap, v 

three multipliers in the harmonic term for displacement, velo- 

v r v 

city and acceleration run thus. — — and—, showing that a 

' W 21 I 

r 
ratio of — which will produce a 5 per cent, difference in the 

position of the piston will bring about a 10 per cent, change in 
the velocity and about 20 per cent, in the acceleration. It will 
now be realized that, when forces are being nicely balanced, 
the importance of the harmonic term must be carefully 
allowed for. 

It is often useful to bear in mind a simple rule for the value 
of the acceleration at the ends of the stroke, i.e. when cot = 0° 
or 180°. From formula (7) it will be seen that this leads to 



dhf 



t 



_ either =—co 2 r( 1 +— . or = — crr[ — 1 + - 
di 2 V 1 A V J 

= T cA(i ± r) 

a very simple rule. i.e. that the acceleration at the end of the 

stroke is more or less than the S.H.M. value bv the fraction - 

I 

of that value. 

112. Connecting Rod Effect. — This is best illustrated by a 
geometrical construction due to Professor J. Harrison. 

The construction is as follows : — 

OB is the crank and AB the connecting rod of which G is 
the centre of gravity. 

OQ and SH are perpendicular to AO. 

Ha is perpendicular to AB. 

SQ and Gg are parallel to AO. 

GU = k 2 AG where k = radius of gyration. 

L"X is parallel to B<7. 

Then TXN parallel to oO is the line of action of the resultant 
of all the forces acting on the rod and its value in ??^ 2 .XN 
where m = mass of rod and q = angular velocity of crank-pin. 
The proof of this construction is given in Perry's Steam Engine, 
and may there be referred to by those interested. 

This diagram enables the direction and amount of the inertia 



CHAP. V | 



THE GAS ENGINE 



165 



forces due to the connecting rod to be calculated for each 
position of the crank. 

If k 2 happens to be equal to the product of AG and GB, then 
GU = k 2 /AG = GB so that the point U would coincide with 
B and the resultant force would pass through and hence 
there would be no " whipping effect " of the rod. One often 




A a N 

Fig. 55. — Resultant of all the Accelerating Forces on a Connecting Rod. 




sees connecting rods produced beyond the crank-pin with the 
object of bringing about this relationship. When it is accur- 
ately obtained it will be found that the period of swing of the 
rod about either big or little end will be the same. 



EXAMPLES 



1. In the case of a single-acting gas engine working on a 4-stroke 
cycle, the mean effective pressure is 40 lb. per sq. inch, the diameter 
of cylinder 8 in., the stroke 8 in., the number of revolutions 360 per 
minute. The governor cuts out 1 explosion every 24 revs. Calculate 
the I.H.P. developed by the engine. 

2. Find the I.H.P. of a gas engine of which the piston is 12 in. dia- 
meter, its crank is 8 in. long, the engine makes 160 revolutions or 80 
c} T cles per minute, and 30 per cent, of the possible explosions are 
omitted. The mean area of all the diagrams on a card taken with a 
120 spring in the indicator as measured by the planimeter is 2-62 
sq. inch ; length of diagram parallel to atmospheric line 4-03 in. 

(B. of E., 1899.) 

3. The mean effective pressure on the piston, both in the forward 
and back strokes, is 62 lb. per sq. inch ; cylinder 18 in. diameter ; 
crank 18 in. long. What is the work done in one revolution ? 

(B. of E., 1906.) 

4. The following data arose in the trials of a gas engine : — Stroke 
23 in. ; diameter of piston 16£ in. ; average M.E.P. 68-8 lb. per sq. 



166 THE INTERNAL COMBUSTION EXGIXE [chap, v 

inch : number of explosions per min. 95 : circumference of brake- 
wheel 24 5 ft. : average net load noted in brake test 484-6 lb. ; average 
speed in r.p.m. 190. 

Calculate (i) The I.H.P. 
ii. The B.H.P. 
hi) The mechanical efficiency per cent. 

5. The following data are taken from a record of a test of a gas 
engine using power-gas : — cylinder diameter = 48 in., stroke = 54 
in., ALE. P. = 75 lb. per sq. inch. Number of explosions per min. = 36. 
Gas used per min. = 1020 cu. ft. Calorific value of gas = 60 C.H.U. 
per cu. ft. B.H.P. = 545. 

Calculate (i) The I.H.P. 

(ii) The mechanical efficiency of engine, 
(hi) Volume of gas used per I.H.P. hour. 

(iv) Volume of gas used per B.H.P. hour. 

(v) Indicated thermal efficiency. 
(vi) Brake-thermal efficiency. 

6. The M.E.P. hi the cylinder of a gas engine is 92 lb. per sq. inch 
when the speed is 166 revs, per min. and there are 72 explosions per, 
min. At the same time, the torque exerted by the crank-shaft is deter- 
mined by a dynamometer to be 1,440 lb. ft. 

Calculate ii) I.H.P. 
(ii) B.H.P. 
(iii) [Mechanical efficiency. 

The cylinder is 14 in. in diameter with 22 in. stroke. 

B. of E.. 1912.) 

7. When a gas engine is running fully loaded the temperature of 
the exhaust gases left in the clearance space at the end of the exhaust 
stroke is 700 : C. and the temperature of the gas and air sucked in just 
before they enter the cylinder is 100° C. The clearance space is a 
quarter of the total cylinder volume < including clearance space). 
Show that the temperature of the gases filling the cylinder at the end 
of the suction stroke will be 170 : C. Assume that no heat is lost to 
or gamed from the cylinder walls during suction, that the pressure 
inside the cylinder is the same as that of the atmosphere, and that 
the specific heat of the exhaust gases and of the incoming charge is 
the same constant quantity. Mech. Sc. Tripos. 1904.) 

8. A gas engine working on the Otto cycle, and running at 200 revs, 
per min.. has a cylinder 1H in. diameter, and stroke 21 in., and 
the compression space is 1 85 of the stroke volume. At the end of 
the suction stroke the cylinder is filled with gas and air at a pres- 
sure of 14-7 lb. per sq. inch, and a temperature of 100 c C. The 
cylinder contents consist of 1 of gas to 10 of air. The calorific 



CHAP. \'| 



THE GAS ENGINE 



167 



Spring Number 
150 




Mean effective pressure 
79.8 



value of the gas is 320 
C.H.U. per standard cubic 
foot. 

The accompanying in- 
dicator diagram is taken 
from the engine : find 
the maximum power and 
the thermal efficiency of 
the engine. 

State how you would 
determine the heat given 
to the cylinder walls dur- 
ing compression and ex- 
plosion. 

9. The indicator dia- 
gram of a gas engine is 
shown in below. The 
equation to the expansion 
curve AB is pv 126 = con- 
stant, and to the com- 
pression curve CD is pv 1A 
= constant. The curve 

AB if produced meets the vertical explosion line in E. The absolute 
temperatures of E, D, and C are indicated on the diagram. Deter- 
mine the thermal efficiency of the cycle, neglecting the rounded 

corners of the diagram, and taking 
the working substance as air. 

(Mech. Sc. Tripos, 1912.) 

10. Crank 1 ft., connecting rod 4-5 
ft. ; what are the accelerations at the 
ends and some other point in the 
stroke, if the engine makes 200 revo- 
lutions per minute ? The piston and 
rod and crosshead are 420 lb. ; draw 
a diagram to show the force in pounds 
required to produce the motion. State 
the scale clearly. 

(B. of E., 1906.) 

11. A piston and rod and cross- 
head weigh 330 lb. At a certain 

instant, when the resultant total force due to steam pressure is 3 tons, 
the piston has an acceleration of 370 ft. per second in the same direc- 
tion. What is the actual force acting at the crosshead ? 

(B. of E., 1902.) 
12. In a gas engine release occurs at seven-eighths of the stroke and 
at a pressure of 40 lb. per sq. inch absolute. The clearance space is 
a quarter of the total cylinder volume. The engine works on the Otto 




168 THE INTERNAL COMBUSTION ENGINE [chap, v 



cycle, explodes every time and is not scavenged. The mixed gas and 
air just before being drawn into the cylinder on the suction stroke has 
a temperature of 100° C. Estimate the temperature of the charge 
filling the cylinder at the end of the suction stroke. 

In making your estimate you will probably assume that gases before 
and after explosion behave as the same perfect gas. How far is this 
assumption correct ? Illustrate the possible errors in estimates of 
temperature based on this assumption by finding their amount in the 
case of a mixture of one volume of hydrogen and five of air. 

~ (Mech. Sc. Tripos. 1904.) 

13. A flywheel 4 ft. diameter in the form of a disc 6 in. thick is keyed 
to the shaft of a high-speed engine. Calculate how much energy it 
stores at 500 r.p.m. and find how much the store of energy is increased 
when the speed increases 5 per cent. One cu. ft. of material weighs 
480 lb. (B. of E.. 1912.) 

14. What must be the size of a flywheel in order that the maximum 
speed may not exceed the mean speed of 60 revs, per min. by more than 
0-2 rev. per min. when the area of the crank-effort curve cut off by 
the mean crank-effort line represents 12*5 ft. tons. 

Give the mean radius of the flywheel and the weight in tons of the 
rim and work out the dimensions on the assumption that the mass of 
the wheel is all concentrated at the mean radius of the wheel and that 
the speed at the mean radius is hmited to 50 f.p.s. (B. of E., 1912. ) 

15. Plot roughly the acceleration of the piston masses in a recipro- 
cating engine from the following data : — 

Stroke 2 ft, 
Connecting rod 4 ft. 
Speed 200 revs, per min. 
Write down the accelerations at the beginning and end of stroke. 

(B. of E., 1912.) 

16. The Figure shows diagrammatically the moving parts of an 
Oechelhauser gas engine. The piston A is coupled direct to the central 
crank-pin by connecting rod B ; the piston C is coupled to the outer 
crank-pins through a crosshead D, side-rods E, and connecting rods 
F. The pistons move in opposite directions, and the explosion takes 




CHAP. Vj 



THE GAS ENGINE 



169 







place between them. The mass of piston C with its attached recipro- 
cating parts is 8 tons, that of A is 4 tons. The stroke of each piston 
is 43 in., and length of each connecting rod is 108 in. Find the magni- 
tude and direction of the unbalanced horizontal inertia force on the 
engine at each dead-point, when the speed is 100 revs, per min. 

It is often assumed in the calculation of inertia forces that the con- 
necting rod may be treated as though half its mass were concentrated 
at each end. Discuss this assumption and explain its practical con- 
sequences in regard to the problem of balancing. 

(Mech. Sc. Tripos, 1913.) 

17. The two 
indicator dia- 
grams * here- 
w i t h were 
taken from a 
gas engine. The 
temperature at 
the point A 
was measured 
directly and 
found to be 
100° C. The 
correspond i n g 
pressure and 
volume can be 
found from the 
diagram. Cal- 
culate the tem- 
perature at the 
point B. What 
further data 
are required to 
enable you to 
calculate the temperature at a point C on the expansion line ? 

The pressure of the atmosphere is 14-7 lb. per sq. inch, and the clear- 
ance is i of displacement volume. 

The cylinder of the engine is 5-5 in. diameter and the stroke 10 in. 
The B.H.P. of the engine was varied, and the speed was maintained 
(by a hit-and-miss governor) approximately constant at 370 r.p.m. 
during the trials. Determine from the diagrams and the following 
data, the frictional H.P. of the engine for each loading : — 

B.H.P 5-51 3-78 1-6 

Explosions per min. . .156 120 75 44 

(B. of E., 1913.) 

* These two diagrams are not really consistent, but the question is 
one worth study. 




CHAPTER VI 

The Gas Producer 

Theory — Typical Suction and Pressure Producers — Tests — 
Costs — Use of Gas Producer tor Marine Purposes — Appendlx 
containing description of mode of operation of suction 
Gas Plant. 

113. Producer Gas. Theory.- — In a steam boiler the energy 
stored up in the coal is liberated by combustion in an atmo- 
sphere containing oxygen. In other words, heat is liberated 
by the combination of the carbon with oxygen first to form 
CO, and then, if enough air be present to add a further atom 
of oxygen to the molecule, to C0 2 . When 12 kg. of carbon 
(that is to say the atomic weight of carbon taken in kilograms) 
are oxidized to CO, 29,400 calories * are given off, and when 
CO, is formed a further 68,200 calories are liberated, 
making a total of 97,600. This means that if the carbon 
be only oxidized to the CO stage not more than about 30 
per cent, of the available heat energy is given up, and that 
by far the most of the available heat is obtained from the 
stage in which CO becomes C0 2 . Even supposing that in 
a given steam boiler the whole of the 97,600 calories were 
given off from each 12 kg. of carbon (neglecting for the moment 
the hydrogen and hydrocarbons in the coal) only a fraction, 
not greater than 70 per cent., usually gets to the water, and the 
balance goes away up the chimney or is lost by radiation. 
With gas producers such heavy losses do not occur. Their 
efficiency depends upon the working process, but it may be 
taken as being seldom less than 80 per cent, and often as much 
as 90 per cent, even when working with anthracite coal and 

* In this chapter the calorie is the kilogram-calorie. 

170 



chap, vij THE GAS PRODUCER 171 

not chemically pure carbon. In a gas producer, air is forced 
or drawn through a mass of highly heated fuel, with the result 
that the carbon is oxidized. Also, in order to keep the tempera- 
ture within reasonable limits, and for another reason to be 
given later, steam is admitted along with the air and both 
together pass upwards through the glowing fuel. 

When the air and steam are forced through by pressure 
the producer is called a Pressure Producer. When however 
they are drawn through by suction caused by the suction 
strokes of the engine, they are known as Suction Producers. 
The theory in both cases is similar. 

It may seem strange to those who approach the subject 
for the first time that it should be possible for the gas given 
off to contain as much as 80 to 90 per cent, of the total 
heat energy in the coal. It would be apparent to them from 
their knowledge of chemistry that even if pure CO came away 
from the producer, and no C0 2 at all, there would be a loss 
of the 30 per cent, of energy liberated when the carbon was 
oxidized to CO, leading to an apparent maximum efficiency 
of 70 per cent. The explanation is that this 30 per cent, is 
not lost. It serves to keep the furnace alight, and to decom- 
pose the entering steam into hydrogen and oxygen, thus — 

2H 2 0-2H 2 + 2 . . . (1) 

and in so doing it stores up 116,400 calories for each 36 kg. 
of steam decomposed. It is easy to see that by suitably balanc- 
ing the proportions of air and steam admitted, it is possible 
to absorb the greater part of the 30 per cent, of energy 
liberated by the formation of CO, and to carry it as potential 
chemical energy to the gas engine, where the hydrogen and 
oxygen can again unite. In reality it is not quite so simple 
as this, because the oxygen from the decomposed steam has 
also to pass over glowing carbon, with the result that a 
further supply of CO is formed. Radiation of heat from the 
producer prevents the efficiency being 100 per cent. 

Following generally the procedure adopted by Mr. Dow son, 
who invented the first of these plants, the reactions may be 
semi-mathematically stated thus : — 

Taking weights equal to molecular weights in kg. 



172 THE INTERNAL COMBUSTION EXGIXE [chap, vi 

Carbon-monoxide is thus formed : — 

2C+O 2 =2CO+58,800 calories . ... (2) 
Carbon-dioxide would be formed thus : — 

C+O 2 =CO 2 +97,600 calories ... (3) 

The former cf these two equations gives a gas having a 
calorific value of about 119 B.Th.U. per cubic foot, but when 
steam is admitted this value rises rapidly owing to the hydrogen 
present. 

As already stated the decomposition of steam fellows 

2H,0=2H 2 -f-0 0—116,100 calories ... (4) 

the negative sign meaning that heat is absorbed and not 
liberated. The oxygen so produced also joins in the re- 
action, so that one of the following formula? 

H 2 O^C=H,-fCO— 28,800 calories . . . (5) 
or 2H 2 0^-C=2H,+C0 2 — 18,800 calories . . (6) 

is followed in the decomposition of the steam. In both 
(5) and (6) an absorption cf heat takes place which allows 
of a balance being obtained by a careful regulation of the 
relative proportions of air and steam admitted. 

114. It is useful to discover what quantity of water is 
theoretically required per pound of coal in order to keep this 
reaction balanced. 

Assume that the reaction follows equations (2) and (6). 
Really it will not follow quite such simple laws, but it will 
approximate thereto if the temperature is high enough.* 
Equation (2) shows that for each 24 kg. of carbon used 58,800 
calories will be liberated, and equation (6) that 18,8C0 calories 
will be absorbed by each 26 kg. of steam dissociated, requiring 
also for its dissociation 12 kg. of carbon. To absorb the 

— q c O A 

whole of the 58.800 calories liberated 36 X — —-kg. of steam 

18,800 c 

would be required. But the steam is not admitted to the 

producer as steam, but as water, and there is therefore the 

* According to Robson. equation | 5) is followed at a temperature 
of about 600"- C. ; and equation (6) from 900 to 1000 : C. At tempera- 
sures between 600 and 1000 both reactions occur. The eqmlibrium 
state is a function of both temperature and time. 



chap, vi J THE GAS PRODUCER 173 

litent heat of evaporation to be considered. Now the latent 
heat of 36 kg. of water- vapour at 20° C. is 21,600 calories, 
and this must be added to the 18,800 calories due to chemical 
dissociation, making a total of 40,400 calories, so that only 

36 X ' - kg. of water would really be required, and this 

40,400 J 

works out at 52-4 kg. of water. The quantity of carbon 

/12 \ 

corresponding to this is clearly 24 -f- ( — X 52 -4 J = 24 -J- 

52-4 
17-5=41-5 kg. of carbon. So that — - or 1-26 kg. of water 
6 41-5 6 

will be required for each kg. of carbon. 

The next point to determine is the nature of the mixture of 

gases given off in this way. Equation (2) shows that for each 

24 kg. of carbon there will be given * off 22-4 X 2 X 1,000 

litres = 44,800 litres of CO Equation (6) adds to this an 

equal volume of hydrogen and half the volume of C0 2 for each 

12 kg. of carbon. Now the quantities in equation (6) must 

clearly be proportional to 17-5 and not 12 kg. of carbon, and 

17-5 
therefore the volume of hydrogen will be X 44,800=65,200 

i _ 

litres and the volume of CO 2 will be 32 , 600 litres. The total will 
therefore be 

CO :— 44,800 litres 

C0 2 :— 32,600 „ 

H 2 :— 65,200 „ 



142,600 litres or 142-6 cubic metres. 

But it must be remembered that in equation (2) oxygen 

is supplied to the extent of 22,400 litres, and that as this 

79 
is drawn from the air it will be accompanied by — X 22,400 

litres of nitrogen which will pass through without change. 

79 
So that to the above table must be added — X 22,400 = 

21 

* Based on the principle that the molecular weight of any gas taken 
in grams will occupy a volume of 22-4 litres. (Some recent work has 
been based on a revised figure of 22-25 litres.) 



174 THE INTERNAL COMBUSTION ENGINE [chap, vi 

84,100 litres of nitrogen, making the total and proportions 
thus : — - 

CO . . 44,800 litres or 19-8 per cent. 

C0 2 . . 32,600 „ or 14-4 per cent. 

H 2 . . 65,200 „ or 28-8 per cent. 

N 2 . . . 84,100 „ or 37-0 per cent. 



226,700 100-0 

Thus 226,700 litres of gas are given off for each 41-5 kg. 
of carbon or 5,450 litres per kg. of carbon, and 5,450 litres 
is of course 5-45 cubic metres. 

What is the calorific power of this producer gas ? The 
N 2 and C0 2 can give nothing. The CO will yield (97,600 — 

29,400) calories for each 28 kg. of CO, or— ^^ = 2,440 

28 

calories per kg. of CO. The H 2 will yield 116,400 calories 

per 4 kg. of gas, or 29,100 calories per kg. of hydrogen. Take- 

1 cubic metre or 1,000 litres of the producer gas. It will 

198 

contain 198 litres of CO yielding X 68,200 = 602 

J 6 22,400 

288 

calories, and of hydrogen X 58,200 = 750 calories, 

J a 22,400 

making a total of 1,352 calories per cubic metre. Furthermore 

the steam formed by the union of the hydrogen and oxygen 

will be capable of yielding up its latent heat, which will add 

21,600 calories for each 4 kg. of hydrogen concerned. Now 

288 
the weight of the hydrogen in 1,000 litres of the gas is 

8 J 6 S 22,400 

X 2 kg. and the calories in the latent heat of the steam will 

288 ft 21,600 10 „ . . , . , . 

therefore be X 2 X - — = 139 calories, which when 

22,400 4 

added to the 1,352 calories found above, makes a total calorific 

value of 1,491 calories per cubic metre of the gas given off by 

the producer. In cases in which the latent heat of the steam 

formed cannot be utilized, it is customary to use the lesser 

value of the calorific constant, and write it down in this case 

as 1,352 calories only, which is nearly 10 per cent. less. The 



CHAP. VI] 



THE GAS PRODUCER 



175 



figure of 1,491 calories per cubic metre corresponds to 168 
B.Th.U. per cubic foot. 

115. Dowson has carried out calculations similar to the 
above for a number of possible reactions, and the following 
tables show some of the results he has found. 



Reaction 

between 

Air and 

Carbon : 

proportions 

of CO and 

C0 2 

formed 

per cent. 

by volume, 

depending 

upon the 

temperature 

of the 

reaction 



CO 




10 
20 
30 
40 
50 
60 
70 
80 
90 
100 



Composition of gas per cent. 

by volume 

(Steam decomposed according 

to equation (6)) 



co 2 


co 2 


CO 


H 2 


100 


28-45 




40-25 


90 


27-8 


0-9 


39-7 


80 


271 


1-9 


3915 


70 


26-3 


30 


38-5 


60 


25-35 


4-3 


37-7 


50 


24-3 


5-85 


36-8 


40 


23-0 


7-65 


35-8 


30 


21-5 


9-8 


34-55 


20 


19-6 


12-4 


330 


10 


17-3 


15-65 


311 





14-4 


19-7 


28-8 



X, 



31-3 

31-6 

3685 

32-2 

32-65 

3305 

33-55 

3415 

350 

35-95 

371 



Steam 

used 

per 

kilo 

of 

Carbon 



Kilos. 



Gas 
formed 

per 

kilo 

of 

Carbon 



Cubic 
Metres 



212 

2-08 
202 



97 
19 
83 
75 
66 
55 
42 
26 



6-54 
6-48 
6-41 
6-34 
6-26 
617 
607 
5-95 
5-81 
5-65 
5-45 



Calorific 
Power of 
Gas made 



Calories 

per 
Cubic 
Metre 



1,243 
1,254 
1,267 

1,282 
1,298 
1,316 
1,340 
1,366 
1,398 
1,438 
1,490 



B.Th.U. 

per 

Cubic 

Foot 



139-7 

140-9 

142-4 

1440 

145-8 

147-9 

150-5 

153-5 

1571 

161-6 

167-5 



This table serves to show the very complete way in 
which Dowson worked out the chemical problems relating 
to producer gas, and the student who wishes to pursue such 
matters further is referred to that writer's interesting book 
on the subject. 

We have now discussed the ideal conditions of working. 
In practice, about the theoretical weight of water is used in 
suction producers. For pressure producers such as the Mond 
producers an excess of steam is admitted in order that the 
temperature of the coal may be kept to a point lower than 



176 THE INTERNAL COMBUSTION ENGINE [chap, vi 

that at which ammonia dissociates, it being a feature of this 
process to recover and sell the ammonia produced from the 
nitrogen contained in bituminous coals ; the effect of this, 
incidentally, is to lower the thermal efficiency of the producer 
to about 80 per cent. 

Equation (5) is sometimes followed instead of equa- 
tion (6) for the decomposition of the steam, depending on 
the temperature of the reaction and the masses involved.* 
Mr. Dowson gives these two comparisons of the theory and 
practice in each case : — 



Theory. 

Gas formed according 
Equations (2) and (5) : — 



to 



Per cent. 
by Volumes. 

CO ■ 39-9 

H 2 170 

N 2 431 



Practice. 

Gas made at Millwall. 

121-3 vols, contain same weight 

of carbon and consist of : — 

Volumes. 

CO 33-5 

H 9 18-6 

Xo 62-8 

CO a 4-7 ' 

Methane 1-7 



100-0 



121-3 

Gas made at Winnington. 

117-6 vols, contain same weight 

of carbon and consist of : — 

Volumes. 

CO 12-9 

H 2 341 

CO., 18-8 

Xo 49-4 

Methane 2-4 



Gas formed according to 
Equations (2) and (6) : — 



Per cent. 
by Volumes. 

CO 19-7 

H 2 28-8 

C0 2 14-4 

N 2 371 



100-0 



117-6 

It will be noticed that an excess 
of air has been admitted in each 
case. 



116. Actual Producers. In Fig. 56 is shown a reproduction 
of a working drawing of a 150 H.P. suction producer made by 
the Campbell Gas Engine Co. The steam required for the 
reaction is derived from the annular boiler surrounding the gas 
producer, and the heat necessary for vaporization is derived 
* See footnote on p. 172. 



CHAP, VI | 



THE GAS PRODUCER 



177 



from the heat of the fuel. This steam passes with the air down 
a pipe leading to the base of the gas producer, and is then drawn 
through the glowing fuel which is maintained at a temperature 
of about 1,000° C. The air and steam on passing through the 
furnace are decomposed in accordance with the equations 
already given, and the hot producer gas then passes through 
a dust trap or separator, and then past a water seal into the 
coke scrubber which consists of a tall vertical vessel containing 
coke upon which a water spray is kept playing. This cools 
the gas, condenses any steam there may be in it and serves 







2 "♦ To En 



gtne. 



/////// 777 / 7? / 77 />///// />////V// 77777777 



Fig. 



56. — Sectional elevation of a 150 H.P. Campbell Suction Gas Producer, 
Fuel is first admitted through the hopper B. Air then enters at A, 
picks up steam on its way and passes by the pipe E to the grate G. The 
gases come away from the upper part of the producer and pass by the 
pipe system shown at D to the Scrubber Chamber, where they are cleansed 
and cooled. The gases are next drawn along the pipe F to the expansion 
box G on their way to the engine. 



generally to cleanse it. Thence the gas passes to a gas box * 
to equalize the pressure, and from that it is drawn into the 
engine as wanted. A full description of how to work such 
a producer is, on account of its possible value to such 
readers who may be unacquainted with the actual working of 
such plant, given as an appendix to this chapter. The above 

* This box should be put as near the engine as possible. 

N 




178 THE INTERNAL COMBUSTION ENGINE [chap, vi 

description applies to a plant using anthracite.* When it is 
desired to use coke as fuel, a sawdust scrubber is usually re- 
quired in addition to the coke scrubber. An outside view of 
a similar plant is also given in Fig. 57. 

There is not a great deal of difference between the different 
makes of suction producer plant. Fig. 58 shows an out- 
side view of a National Gas Engine Co. type, similar to that 
which was awarded the gold medal at the Royal Agricultural 
Society's Trials in 1906. Its internal arrangements are much 
the same ao those already described, except that the vaporizer 




Fig. 57. — Outside view of 80 B.H.P. Campbell Suction Gas Plant, 
small size of Producer for the amount of power produced. 



Note 



is fed with water which has first been heated by being passed 
through a pipe in the gas outflow passage and is then vaporized 
on the " flash " system. 

Pressure producers are worked on much the same general 
principles, except that the air and steam are forced through 
the coal instead of being sucked through. In general, too, 
they are for much larger plants. Suction producers are usually 

* Bituminous fuels cannot be used in suction gas producers, unless 
of the specially designed type made by Dowson and a few other makers, 
and such producers are less simple to operate. 



CHAP. VI] 



THE GAS PRODUCER 



179 



for quite small outputs — commonly about 30 or 40 H.P. 
and rarely going beyond 500 H.P., whereas the power from 
pressure producers may run into thousands of horse-power, 




5 

d 
_o 
'43 
o 

a 

© 

'So 
a 



<3 

e 

a 
o 

'-3 



00 



and the latter are therefore of a much more extensive nature, 
and a good deal more complicated, especially when a feature 
is made of by-product recovery. 

117. Tests. It will be of interest to give here some figures 



180 THE INTERNAL COMBUSTION ENGINE [chap, vi 

from the tests held on suction producer plant in 1905 by the 
Highland and Agricultural Society of Scotland, and in 1906 
by the Royal Agricultural Society. 

In the 1905 trials ten complete plants, exhibited by six 
different firms, were sent in for the competition. Particulars 
of these plants are given in the following table (see p. 181). 

The result of the trials was given in the Judges' report,* 
of which the following contains an account. 

Each plant was allowed half an hour of steady working 
before the actual power test, at the end of which the plant 
was brought back as nearly as possible to the same condition 
in respect of fuel, etc., as it was at the beginning of the trial, 
and the actual weight of fuel supplied in the interval was 
taken as that consumed by the plant during the power test. 
The obviously weak point in this procedure was that it was 
quite impossible to determine absolutely whether the plant 
was realty in the same condition at the end of the trial as it 
was at the beginning. By running the test for a long enough 
time, however, any slight error in this respect could be rendered 
of little importance, and probably the method adopted was 
the best one. The alternative would have been to start the 
producers up from rest, and note the fuel put in, then at the 
end of the trial, note the proportion in the producer which 
had not been burnt, subtract the two, and add to this any fuel 
which had been introduced during the test. This procedure 
was adopted at the R.A.S. trials in 1906, except that the fuel 
consumed when the producers were banked up all night was 
also included, so leading to the disadvantage that it did not 
give a real fuel economy test. Also it was extremely difficult 
to tell at the end of the trial how much of the fuel left in the 
producer could properly be said to be " unburnt." 

In the Scotch trials it was found that the coal per 
B.H.P.-hour at full load varied from 1-25 to 0-84 lb., and at 
half load from 1-55 to 0-91 lb. This was for the 8 H.P. sizes. 
For the larger, 20 H.P., plants the fuel per B.H.P.-hour at full 
load varied from 0-93 to 0-77 lb. and at half load from 1-08 to 
0-92 lb. These results serve to show how economical the 
suction producer plant is when compared with steam engine 
* Engineering, November 17, 1905, 



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182 THE INTERNAL OOMBt >TI< X ENGINE Yttap vi 



plant of the sarue output : the latter would consume any- 
thing f : : m 2 1 tinies to 4 tin:— ;-. - much fuel per B.H.P. Cither 
interesting figures reported by the Judges are that the capa- 
city of the producer per declared B.H.P. varied from 0-124 
cu. ft. to 295 eu. ft. for the 20 HP size, and from 0-161 
c-u. ft. to 0-372 cu. ft. for the 8 H.P. size. Each of these 
figures show a ratio of about 2-3 to 1 and the price of the 
plants varied also but in not - : great a ratio. The variation 
in cubic feet capacity per B.H.P. was an indication that 
little had then been done towards standardization of design. 
118. The tests carried out by the R.A.S. in 1! -xere 
considerably more elaborate, and. as already stated, a different 
procedure was followed. The report of the Judges had been 
published and. although in some aspect? it may be said to e 
controversial, it is certainly worth study. Fourteen plants 
were entered for trial and all but three ran through to the 
finish. The capacity in each case was 15 to 20 H.P. X A 
list of the plants with their leading dimensions and other 
particulars is given here — 



Producer. 


- 


Revs 


~ :-"" 


in! 


- ' ~ ". ■ 

C.i.r. 


National 


National . . . 1 


18 


:■: 


_ 


Jj:~=:i- 


ri-rral 


"_i 


12 


. 


Paxmaii 


Paxmaii . . 220 


15 


n 


1-5 : 


r»:~i:- 


_ . : nal . 




:;•■:■ 


IS 


:: 


20 


Campbell . 


ipbell 




_. 


19 


9i 


18 


'. :. Ill" ". -r 11 . 


^ipbell 




: : - : 


.. 


:■: 


::■ 


Dudbridge 


Dodbrid^ 




ac : 


IT 


n 


. 


M-: sey 


idner . 




. 


18 




. 


Hindley 


Hn_:.l-- 






■:-:: 


7 


— 


16 


Kynoch 


Ktti: ::: 






u 


lr 




IT 


Newton 


1 '-—-. m 






.. 


:> 


;- 


I 


Fielding 


~lrl """"" : 






22 


^ 


y* 


18 


'. : 3B ley 


: ssley 






_. 


21 


- 


17 


Crossley 


C : : ssley 






1-0 


21 


8| 


15 



Measurements made of the fuel and water consumption 

showed figures ranging from 1-47 to 104 lb. of anthra 
: lie aieac averaged about SJ sq. ins. per B.H.P. 



(hap. vi] THE GAS PRODUCER 183 

per B.H.P.-hour and from 3-61 to 0-73 gallons of water per 
B.H.P.-hour. The enormous variation in the quantity of 
water required was very striking, and it showed that there 
was a considerable difference in the manner of operation of 
the various plants. As the water required for steam making 
is very small, practically the whole of the above difference 
must have been due to the different quantities taken by the 
scrubber. 

The Judges published the following conclusions as a result 
of the consumption trials — 

That with a good suction producer plant, working contin- 
uously, at the specified loads and under the best conditions, 
the following results may be anticipated : — 

With Anthracite. 

Full load : 1-1 lb. per B.H.P.-hour including fuel needed for 
starting, and for banking during the night. 

Half load : 1-6 lb. per B.H.P-hour including as above. 

Water : 1 gallon per B.H.P.-hour at full load and j- gallon 

at half load. 

With Coke. 

Full load : 1-3 lb. per B.H.P.-hour including fuel needed for 

starting. 
Water : 1^ gallons per B.H.P.-hour at full load. 

Professor Dalby * also recorded as a result of these trials 
that — 

" Assuming a 20 B.H.P. plant to start on Monday morning 
with an empty producer, and to run ten hours per day on 
full load for a week, banking the fires at night, the consump- 
tion of anthracite peas would be about half a ton for the 
week, and about § ton if the average load is about half full 
load. With coke the consumption is about 25 per cent, 
more. From 2,000 to 3,000 gallons of water per week are 
required for a 20 B.H.P. plant to provide water for the scrubber 
and the producer, and of this by far the larger part would be 
used in the scrubber." 

Tests were also made of the times taken to start up and 
* B. A. paper, August, 1906. 



184 THE INTERNAL COMBUSTION ENGINE [chap, vi 

to change load. As a result of their investigations the Judges 
awarded the premier places to the National and Crossley plants. 
The Judges were Professor Dalby and Capt. Sankey. R.E. 

119. Test of a Dowson Suction Gas Producer Plant. — The 
following account of tests on two Dowson Suction Plants is 
extracted from Mr. Dngald Clerk'- 1904 *' James Forest " 
Lecture before the Institution of Civil Engineers. The tests 
were carried out by Mr. M. Atkinson Adam. B.Sc. Assoc. M. 
Inst. C.E. The first plant was adapted for a working load 
of 40 B.H.P. and the second for 30 B.H.P. In each ease the 
producer was started up cold, and run on test for fully eight 
hours. At the start air was blown in by a small hand-power 
fan and after ten minutes from lighting up the gas was of a 
proper quality. The gas was then sucked through by a fan,, 
which represented the action of a gas engine operating under 
a constant load sucking gas from a producer in the usual way. 
Thence the gas passed to a gas holder. Analysis samples 
were frequently taken and the anthracite analyses were under- 
taken by Mr. Bertram Blount. E.I.C.. Assoc. Inst. C.E.. whilst 
the eras analyses were carried out by Mr. Horatio Ballantvne. 
F.I.C. The heat efficiency of the producers was found in two 
ways : — 

(1) Counting in the fuel used in the starting up operation 

which includes that necessary for the heating up of 
the plant. 

(2) Omitting the first two hours of the test, and so giving 

the plant what may be termed a " flying start." 

The quantities of water used are very interesting. The 
figures showed that for vaporization, the 40 B.H.P. plant 
used about 30 lb. per hour, whilst the 30 B.H.P. plant used 
about 20 lb. per hour. Eor the scrubber, the 40 B.H.P. plant 
used about 400 lb. per hour, and the 30 B.H.P. plant used 
about 3 SO lb. per hour. This -how- how small a proportion 
of the total water consumption is needed for vaporization. 
The anthracite used was of an ordinary commercial kind., 
costing 14-5. 6rf. per ton at the pit. and about 24-5. per ton 
delivered at Basingstoke. The efficiency figures for the two 
producer plants were found to be 



chap, vi] THE GAS PRODUCER 

"Standing start" . | 3() BHp ' 
" Hying Bfcwt' • {30 B.H.P. 



185 



85 per cent. 
75 per cent. 
89 per cent. 

86 per cent. 



Reference should be made to the paper for detailed figures, 
but it may be mentioned that the gas was found on a general 
average to have a calorific value of 135 B.Th.U. per cubic 



and have a compositi 


on as iollows :— 




H 2 


. 15-5 


per cent. 


CH 4 


1-2 


5 5 5 5 


CO 


. 20-0 


5 5 5 5 


co 2 


70 


55 55 


2 


0-5 


55 55 


N 2 


. 55-8 


55 55 



100-0 



120. Tests of Pressure Producers.— In 1904 some exhaustive 
tests were made in America on the results of employing differ- 
ent varieties of bituminous coal in pressure producer plants 
and in steam engines, and it is worth while to give a brief 
account * of some of the figures obtained (see p. 186). 

In each case the output was about 200 E.H.P., and in 
most cases the length of the trials was from 10 to 30 hours. 

Mr. Shober Burrows has reported the result of a 24 day test 
undertaken in 1906 on a pressure producer plant operating 
with bituminous fuel. Analysis of the fuel showed — 



H 2 


. 


. 14-68 


Volatile 


combustible . 


. 30-98 


Fixed carbon 


. 42-93 


Ash . 


.... 


. 10-08 


S . 


.... 


1-33 




10000 


B.Th.U. 


per lb. . 


= 12,343. 



* The Times Engineering Supplement, January 23, 1907. 



18< THE INTERNAL : )MBU$T10E ENGINE fen 













— i. - 


Rartu 






- 1- ■• T 


TT ~ 






: V 7 






_.._. 




' "" 




Kind off Goal 






- . . . 




_T . i-I. 7 


± - ii " 


Z ■'•' '. 






I-: 


I 




Bitmrriri . 


A^ 


4 . - 


: 




Black lignite 


C :".:rs-i: . X:. 1 . 


i y 


: ": 


. ?: 


BitTimui . 




7"- :is, No. 3 . . 


4 ;-4 




. 42 








.. 4 . . 






- 73 


• 






! Twdmim. XoJl 


4-13 


"_ ;-: 


. 14 








_ 


4 ; : 


1 " ': 




. 






Ind. Tr:: No. 1 . 


4 H 


1 - 


2-21 


»? 




4 


4 :-4 


1-43 


324 






I : t 


4 


1-73 




- 




Kansas , Mi 


343 












71 No. 3 


4-22 


1-91 


2-21 


M 




MisBOTJui, 3Hol 2 . 


4-93 




_ — 


n 




W. Virginia, Ma. 1 - 


3-90 


"_ 




• 




_ 

- 


! 52 


: _} 








.. " 


3-53 


1-46 








- 


3-63 




2-04 


ra 




if . 


3-46 


1-40 








. 12 


3-53 


: : 


. : " 






WyOH l - 


----- 

















The gas left ~i-- generator at about 644 
seal to the scrubber. 



water seal to the scrubber. Thence to a centrifugal tar ex- 
tractor. The calorific value of the gas was found to be 156 
B.Th-U. per en. ft. and its composition ws 



Ethylene 

Methane 
M a - 



f . 






100-0 



chap, vi] THE GAS PRODUCER 187 

About 143 lb. of tar was extracted per ton of coal used in 
the producer, whilst the approximate figures show that an 
average of 1-39 lb. of coal was used per B.H.P.-hour. As 
this plant ran for 24 consecutive days without shutting down, 
it is evident that continuity of operation could be practically 
achieved. 

The whole of these tests go to show the great fuel economy 
obtained by the use of gas plant as contrasted with steam- 
plant. Another feature in which the gas plant has the advan- 
tage is in the smallness of the stand-by losses. When a boiler 
is banked up for the night it consumes a very much larger 
quantity of coal during the period of banking than a producer 
plant of the same output would require. Actual measurements 
of this nature are recorded by Mr. Dowson in his book 
on Producer Gas, and it was found that in the case of 
steam power, the consumption of fuel per standing hour 
was 71-5 lb., and in the case of gas power, 3-5 lb. only, which 
shows a ratio of about 20 to 1 . And since each of these figures 
is the mean of several tests, they are not open to the criticism 
that they represent isolated cases only. 

It will be of advantage to record at this point what are 
the chief objects to be achieved in the design and working 
of producer plant — 

(a) A fairly deep fuel bed should be allowed for, otherwise 
the air may blow through in thin places, and so lead 
to local variations in the temperature. 

(5) Provision of some sort must be made to prevent caking 
or cavitation of the fuel. 

(c) Fuel must be fed in and ashes removed in such a way 

as not to render the process discontinuous or inter- 
mittent. 

(d) Leakage of gas from pressure producers must at all 

costs be avoided, as the gas contains a large pro- 
portion of poisonous CO. 

There are a good many makes of pressure producer plant, 
and some are adaptable for by-product recovery. Among 
the latter one of the most prominent types is the Mond pro- 



188 THE INTERNAL COMBUSTION ENGINE [chap, vi 

ducer, which is being used on a large scale in South Stafford- 
shire. Here ammonia in the form of ammonium sulphate 
(Am 2 S0 4 ) can be produced as a by-product and sold for a 
considerable amount — often more than enough to pay the 
coal bill. In this process, as has already been explained, 
the temperature of the producer must be kept low. and to 
do this, large quantities of steam are used, as much as 2^ lb. 
per lb. of coal. This has the effect of course of reducing 
somewhat the actual efficiency of the gas producer and of 
raising the percentage of hydrogen present, but not to such 
a point as to introduce trouble in a suitable engine. 

121. Percentage of Hydrogen. — The percentage of hydro- 
gen present in the gas to be employed in a gas engine regulates 
the amount of compression which can be used. A good com- 
pression is essential for high efficiency, but if the proportion 
of hydrogen is high the danger of pre-ignition has to be 
guarded against. The following table taken from a paper 
by Mr. J. R. Bibbins * shows the proportion of hydrogen 
present in various kinds of gas and the calorific value of the 
gas when taken alone, and when taken with its theoretically 
requisite proportion of air- — 



Gas 



Natural Pittsburg . 

Oil 

Coal-gas .... 
Carburetted water gas 
Water gas 
Producer, hard coal 

„ soft . 

,, coke . 




Attempts have been made to reduce the proportion of 



* " Fuel Gas for Internal Combustion Engines," Gassier s Maga- 
zine, 1906. 

f Based on theoretical air for combustion. See also par. 143. 



CHAP. VI] 



THE GAS PRODUCER 



189 



hydrogen by admitting some of the exhaust gases into the 
producer instead of water vapour. In this case the dissocia- 
tion of COo replaces that of H 2 0. This process is called the 
" straight carbon-monoxide gas producer." It is claimed 
to work very well and to permit of very high compressions 
being used. The gas has a calorific value of 105 B.Th.U. and 
a composition of : — 



CO 


26-95 per cent 


H 2 


0-20 


co 2 


1-75 


CH 4 


0-50 


N 2 


69-30 


o 2 


1-30 



122. Comparison of Costs.— The following interesting com- 
parison has been drawn up by Mr. L. Andrews * and is well 
worth study. 



Capital Cost of 16,000 K.W. Plant. 



Engines and electric generators 

Boilers, feed-pumps, coal handling 
plant, etc 

Producers, gas-cleaning and coal hand- 
ling plant, with all pipes. 

Engine-room, building, cranes, and en- 
gine foundations 

Switch-gear and wiring for ditto . 



Allowance for contingencies, 5 per cent. 



Capital cost per K.W. installed . . 



Steam 
Turbines 



£ 
96,000 

81,000 



18,000 
5,250 



£200,250 
10,012 

£210,262 
£131 



Gas 
Engines 



£ 
161,700 



77,700 

42,000 
5,250 



£286,650 
14,332 

£300,982 
£18-88 



* Electrical Engineering, October 24, 1907, and S.A., January 30, 
1908. 



190 THE INTERNAL COMBUSTION ENGINE [chap, vi 



Ruxxixg Cost ox 100 per cent. Load Factor. Anhstual 
Output = 140.000.000 K W. Hottrs. 



Fuel, 165,000 tons at 10s 

Fuel, acid, stores and repairs for pro- 
ducers, less sale of by-products . 

Labour 

Repairs of turbine plant, including 
boilers, etc 

Repairs of gas plant (excluding pro- 
ducers) 

Oil, waste, and stores (excluding pro- 
ducer stores) 

Interest and depreciation at 10 per cent. 



Totcl cost per K W. hour 



Steam 
Turbines 


Gas 

Engines 


£ 

82,500 


£ 


7,000 


28,250 
9,000 


8,750 


— 


— 


6,000 


1.750 
21,026 


4,37 ) 

30,098 


£121.026 
0-204d. 


£78.118 
0135d. 



Mr. Andrews also takes the case when the load factor is 
only 15 per cent., and in that condition of running the costs 
per KW.-hour came out at 0- 545(7. for steam turbines, and 
0-566ri. for gas engines. These rates are nearly the same, but 
with rise of load factor the balance would soon turn in favour 
of the gas plant. Mr. Andrew's estimate of the capital cost 
of the gas plant, viz. nearly £19 perKW., would now be con- 
sidered unduly hio:h. 

123. The Use of Gas Plant for Marine Propulsion has been 
discussed before several engineering societies. 

Mr. J. T. Milton in his 1906 paper before the Institution 
of Civil Engineers stated that he was led to give attention 
to engines of this kind in connexion with proposals to fit 
them in vessels classed with Lloyd's Register. The paper 
deals with engine problems only, and assumes that a proper 
and suitable type of producer capable of using cheap fuel 
would before long be available. The writer of the paper specifies 
the following conditions which must be satisfied by a successful 
marine engine — 

(a) The engine must be reversible. 



chap, vi] THE GAS PRODUCER 191 

(b) It must be capable of being stopped quickly and of 
being started quickly either ahead or astern. 

{(') It must be capable of being promptly speeded to any 
desired number of revolutions between dead slow 
and full speed, and of being kept steadily at the re- 
quired speed for any length of time. " Dead slow ' 
ought to be not faster than one-quarter of full speed, 
and should be less than this in very fast vessels. 

(d) It must be capable of working well, not only in smooth 

water, but also in heavy weather, in a seaway in which 
the varying immersion of the propeller causes rapidly 
changing conditions of resistance. 

(e) All working parts must be readily accessible for over- 

hauling, and all wearing surfaces must be capable of 
being promptly and readily adjusted. 
(/) The engine must be economical in fuel, and especially 
so at its ordinary working speed. 

Certainly no existing engine complies with all these con- 
ditions, and reference should be made to Mr. Milton's paper 
for a discussion of the difficulties : some curves are there 
given showing the different turning moment curves for different 
arrangements of engine. 

Another paper is that read by Mr. J. McKechnie before 
the Institution of Naval Architects * under the title " Pro- 
pelling and Ordnance Machinery of Warships," and a portion 
of it deals with gas engine propulsion. It was stated that 
at the Vickers Works at Barrow-in-Furness there had been 
constructed internal combustion engines of a power equivalent 
to about 40,000 I.H.P., and that for three or four years almost 
continuous research work had been undertaken. As a result 
of the experiments a 2-stroke engine has been designed. This 
engine, it was claimed, could be worked by producer gas, oil, or 
compressed air, was reversible, and could take gas direct from 
a pressure producer without any scrubbing being necessary. 
To prevent the poisoning of the crew by the leakage of the 
gas from defective joints the pipes were jacketed with air under 
compression. 

* Proc, I.N. A., 1907, 



MS THE DTTEEXAL COMBUSTION EN'GIXE [cmp. vl 

Not only would the introduction of jaa engine- in 
ship propulsion lead to a gain of space and dead weight - 
allowing the offensive or defensive materiel to be added t 
but the better disposition of its parts, and the absence of 
funnels would admit of a great improvement in respect of an 
actual increa - - ..... the number of guns which could tire on 
either broadside. In the proposed plan of battleship con- 
struction, the . >rod - - ire shown divided into twi sefe 
well on either side of the ship, and the propelling machinery 
is shown well aft. The deck is clear for gun barbettes. Mr. 
Milton, gives the following comparative table illustrating the 
superiority of the gas engine plant so far as area occupied, 
weight and fuel consumption are concerned — 

:zpasiscz~ :z zz -zi . etc., j - zz^_z: k« .-_ zz >rc 



IM. ±L»4Ufck. FOE lb UUU H.P. 


h>A)"l'l KSH1P 






l - ...: Kngm - 


Rhgroe 


Oil Ekgme 


I.H.P. available lor pro- 








peTlrnsz the ship . 


L6.000 


16. 


if 


e zlit of machinery, in- 








cluding nsiiaL auxiliaiz - 








bat not deck machinery 


1.585 tons * 


1.105 tons f 


" : - as : 


LKP. per ton of macnrz- . 


10-1 


11 — 


21-33 


Area occupied by machin- 








~ i mes and boilers 








i i zrodiicers .... 


" . " - :- 


z 


4.1" - z 


Area per LH.P. 


- j - . ft. 


.. ft. 


.'' - . ft. 


7 z - [ jonsnm ption in lb. per 








I.H.P. nonr — 








Afe full power. 


: ; lb. 


1-0 lb. 


! ; lb. 


-z ~ - foil power . 


. § lb. 


115 1b. 


' a lb. 



A further paper is Mr. A. Vermeil Coster- "e~ore the 
Manchester Association of Engineers, dated VI- ' As 
Mr. Coster had much experience with marine steam engii: - 
anl spent many years with Messrs. Crossley Bros 

* Includes ' ires ba boilers 

seta zd piping. 1: at sal real in producers. 
I .. .. • ■ - zd piping 






chap, vl] THE GAS PRODUCER 193 

experience gives his conclusions much authority. The 
following arc the advantages claimed for the gas engine — 

1 . The ship driven with half the amount of fuel. 

2. Standard losses reduced over 75 per cent. 

3. Working pressure confined to the engine cylinders. 

4 . No boiler tubes or main steam pipes to burst, nor furnace 

crowns to collapse. 

5. No priming in a heavy seaway, or water hammer in 

pipes and cylinders. 

6. No more difficulties with the firing of boilers on a beam 

sea. Gas producers may be charged only twice every 
twenty-four hours, and the rolling and pitching of 
the vessel is rather an advantage than otherwise in 
assisting the fuel down from the charging hoppers. 

The three main difficulties in the way are — 

(1) The construction of a gas producer able to gasify all 

grades of bituminous coal. 

(2) A simple method to cleanse the gas from tar, either 

before the introduction of the fuel into the producer 
proper ; when in the producer ; or after the gas has 
left the producer on its way to the engine. 

(3) Perfect control of the gas-propelled vessel in starting, 

stopping, reversing and running at all speeds. 

The first of these difficulties obviously is avoided if coke or 
anthracite is used in the producer, but this solution is neither 
economical nor satisfactory on other grounds. Bituminous 
coal must be regarded as the source of the power to be used 
for ship propulsion. Mr. Coster stated that in his scheme 
for the cargo vessel Lord Antrim the producers were worked 
by means of a down-draught at the top, and an up-draught 
at the bottom, which met at the centre and the gas was drawn 
off by suction. The gas was then thoroughly sprayed and 
cleaned by being passed through coke, sawdust and wool 
wood scrubbers. 

The reversing difficulty can be met in small engines by the 

o 



. I THE DTTEEXAL COMBUSTION ENGINE [chap, vi 

use of a reversible propeller, but for obvious reasons this 
would not do in the case of large engines. For powers up to 
H.P. gearing may be introduced to effect a reversal in 
the direction of propeller rotation, just as in a motor car. but 
this cannot be used when the power transmitted is really 
large. 

One of the great difficulties in connexion with the utiliza- 
tion of the gas engine on board ship lies in the fact that when 
the speed of the ship is decreased, the resistance to motion 
is decreased at a far greater rate, and this means that the 
mean effective pressure on the piston must be capable of very 
considerable reduction. When an attempt is made to get 
very low mean effective pressures in a gas engine, the engine 
is liable to stop altogether — in fact the gas engine as at present 
devised is not stnieiently elastic in its manner of working to 
make it an effective rival to the steam turbine for marine 
purposes. The difficulty may be solved by driving generators 
from the gas engines, so producing electric current which can 
be used in motors driving the screw propellers, but this requires 
a great weight of machinery, and is costly. 

1&4. The well-known firm of Thornycroft have been working 
a good deal at the problem of adapting gas engines to ship 
propulsion, and an illustration is shown in Fig. 59 of an 
engine they are interested in. The chief difficulty is to devise 
a suction producer which will work with bituminous or caking 
coal without the necessity of being provided with apparatus 
for the extraction of tar and other by-products. The tar often 
amounts to 4 or 5 per cent, and may be as high as 15 per cent. 
It is therefore necessary to arrange the producer so that all 
the tar produced is consumed before it leaves the producer. 
This can be done by feeding in the fresh fuel from below a 
that the heavy hydrocarbons given off from it are consumed 
as they rise into the hotter part of the tire. To save weight 
and space Herr Capitaine has hit on the idea of cleaning the 
gas by introducing a fine water spray, which mixes with the 
dust and other impurities, making a kind of fog. This fog 
then passes into a centrifugal machine which is driven fast 
enough to throw out the impurities and leave clean gas in the 
middle, which is then, drawn off by the engine. Mr. J. E, 



(HAP. VI] 



THE GAS PRODUCER 



195 




Fig. 59. — Two-cylinder Suction Gas Engine and Producer for Marine Pur- 
poses. (By courtesy of Messrs. J. I. Thornycroft & Co.) 

Thornycroft * has given the composition of such gas as 
follows : — 

C0 2 

CO 

CH 2 

H 2 . 

N 2 . 



6 


per 


cent 


. 25 


5 5 


5 5 


1 


5 5 


5 5 


. 14 


55 


55 


. 54 




5 5 



100 
He also remarks that " it will be realized that the size of 
the producer for a given power is comparatively small when 
* Paper on " Gas Engines for Ship Propulsion,'' read April 5, 1906, 



196 THE INTERNAL COMBUSTION ENGINE [chap, vi 

it is known that the area of the fire grate necessary is only 
0-05 sq. ft. per H.P., whereas the average for an ordinary 
natural-draught steam boiler, burning 15 lb. coal per sq. ft. 
grate area, would be 0-2 sq. ft. per H.P." 

The following test result is recorded by Mr. Thornycroft : — 
' Tests were made on November 8, 1904, with the Gastug 
No. 1 and EJfriede, a steam tug of very nearly the same dimen- 
sions and power. The Gastug No. 1 is 44 ft. 3 in. long by 
10 ft. 6 in. beam, and is fitted with one of the four-cylinder 
70 H.P. suction gas plants. The Eljriede is 47 ft. long by 
12 ft. beam, and is fitted with a triple-expansion steam engine 
developing 75 H.P. At the towing meter the Gastug No. 1 
attained a maximum pull of 2,140 lb., and the Eljriede a maxi- 
mum of 2,020 lb. A run from Hamburg to Kiel and back 
was made by these two boats, during very stormy weather, 
at a maintained speed of 8 J knots. The consumption of fuel 
was measured for a period of 10 hours, and was as follows — 
For the Gastug No. 1, 530 lb. of German anthracite : for the 
Eljriede, 1,820 lb. of steam coal. This shows an economy of 
1 to 3-44 in favour of the gas plant." Notwithstanding these 
successful efforts the difficulties to be solved before this method 
of ship propulsion becomes at all general are very great.* 

125. Low Coal Engine. — An engine has been introduced 
by A. M. Low in which a special cylinder head contains a 
miniature gas producer, so that small coal can be fed direct 
to the engine. The coal passes down vertical tubes heated 
externally by the exhaust gases ; through these tubes is 
passed a stream of air and steam in the same proportions as in 
a suction gas producer. It is claimed that an experimental 
plant used only about 0-5 lb. of coal per B.H.P. hour, but 
detailed figures are not given of this test.t 

APPENDIX A 

The folio whig is a description of the operation of a typical 
suction producer plant. 

The suction type of gas-producing plant in question (Campbell) 
consists essentially of two mam elements, a gas producer and a 

* See Internal Combustion Engineering, p. 33, April 29, 1914. 
j The Engineer, Xovember 15, 1912. 



chap, vi] THE GAS PRODUCER 197 

gas scrubber. In addition to these there is a simple form of separ- 
ator through which the gas passes on its way from the producer 
to the scrubber, and in which it deposits the heavier particles of 
dust which are carried over from the producer. A gas box is also 
provided between the scrubber and the engine, to act as a reser- 
voir, from which the engine can draw a regular supply of gas. 

1. Method of Gas Production. — -In this method of gas production 
air and steam at atmospheric pressure are drawn through incan- 
descent fuel by the motion of the engine, the oxygen, hydrogen 
and carbon combining in the producer to form a combustible gas 
which is suitable for power purposes. No boiler for providing 
steam under pressure is required, and no gasometer, the engine 
generating its supply of gas by the motion of the piston in the 
cylinder. The fuel used must be anthracite coal or coke (bitu- 
minous coal must not be used). The steam is generated in an 
evaporator which is heated b} r the fire in the gas producer. The 
air is drawn into the producer over the surface of the heated water 
in the evaporator and in passing takes up the steam which it then 
carries through the producer. 

2. General Instructions. — The coal used should be passed through 
a sieve and no pieces under J in. (5 mm.) should be used. The 
most suitable size is f in. to 1 in. (16 mm. to 25 mm.). Coal dust 
is not only of no value, but it tends to stop up the pipes and 
interfere with the working of the plant. The fuel should not be 
imoistened before it is used. All the moisture required should be 
provided in the form of steam and pass through the fire in the 
ordinary way as described below. The evaporator should always 
be kept full of water to the overflow pipe. A water supply must 
be provided for the evaporator and the coke scrubber, and a drain 
to carry away the water from the scrubber. In any installation 
of this type, the engine should be erected as close to the pro- 
ducer as practicable so that the connecting pipes between the two 
are as short and direct as can be arranged. 

3. To Start the Gas Producer after Erection or Cleaning. — Before 
starting it is of the greatest importance to see that all the piping, 
cocks, and various vessels which go to make up the gas-producing 
plant should be air tight, as the apparatus when in operation is 
subjected to an excess of atmospheric pressure from without. If 
the various parts of the plant are not air tight, the air which leaks 
in will interfere with the quality of the gas and make it poorer. 
For this reason the whole apparatus should be tested after erection 
to prove the soundness of the joints, the test being carried out as 
follows : Referring to the illustration, if all the openings are closed 
except the cock B, and air is then blown into the apparatus by the 
hand fan A, the various joints can be tested with a light. If air 
or gas escapes from the joints it will be at once detected. This 
test should be made periodically to see that everything is in order. 



198 THE INTERNAL COMBUSTION ENGINE [chap, vi 

It may he carried out at anytime after cleaning, and when every- 
thing is proved to be in good working order the engine should be 
made ready for immediate use when the gas is available. 

Provided that all the joints are sound and tight, the water should 
now be turned on to the coke scrubber by means of the tap C until 
it overflows through the pipe D provided for that purpose. It is 
essential that the scrubber should contain sufficient water to seal 
the gas inlet. 

Water should then be admitted to the evaporator F by means 
of the tap G until it just overflows in drops by the pipe T provided 
for that purpose. This overflow should be very slight before start- 
ing and must be regulated from time to time when running accord- 
ing to the load on the engine as described below. The taps C and 
G and the cock H should now be closed. The cock B and the cock 
J on the waste pipe K should be opened. The fire door L and the 
ashpit door M should then be opened and a fire of wood or coke 
started in the gas producer. Ordinary bituminous coal must on 
no account be used. When the fire is burning up well anthracite 
coal should be added through the hopper N in small quantities 
from time to time as the whole mass of fuel becomes incandescent 
throughout, this being continued until the gas producer is full to 
the level of the bottom of the gas pipe P. The fire door L and ashr 
pit door M should be closed as soon as the coal is well alight. The 
hand fan A must be used for the purpose of blowing up the fire 
when starting, the whole of the products of combustion being blown 
by its means through the gas pipe P. separator B and uptake pipe 
K to waste, the cock J being open during this operation. Supposing 
the fire to have been lit for. say. fifteen to twenty minutes, and 
the hand fan to have been in operation during that time, the quality 
of the gas which is being made can now be tested by partially closing 
the cock J and thus passing the gas through the scrubber and gas 
box to the test cock Q. The nearer this test cock is placed to the 
engine the better : it can be placed at any convenient point in the 
gas pipe, between the engine and the gas box, for example. Before 
passing the gas through the scrubber the water must be turned on 
to the scrubber, by the tap C. The blowing will have to continue 
for a few minutes until the scrubber and gas box are cleared of air. 
and gas ha> been blown in to take its place. A fight should then 
be placed to the test cock Q and the gas if of a good quality will 
burn with a steady flame. If the coal is of good quality the gas 
will burn with a long flame, orange red in colour,, and one which 
does not go out. With some coals it is difficult to produce anything 
but a blue flame, but as long as the gas burns steadily it will 
generally be found that it is of sufficiently good quality to start 
the engine. 

Caution. — When testing the gas. as described, care must be 
taken to turn the fan at a steady and even speed. Under no cir- 



CHAP. VI] 



THE (J AS PRODUCER 



199 



cumstances should the fan be stopped while the gas is burning at 
the test eock or the pressure will at once fall and the flame will 




probably be drawn back into the gas box and fire the gas in the 
gas box and scrubber, the explosion caused thereby blowing the 
water out of the water seal and possibly doing other damage. 



200 THE INTERNAL COMBUSTION ENGINE [chap, vi 

On the other hand the fan must not be blown too hard or the 
_ - will be forced out through the water seal at the bottom of the 
coke scrubber. 

The tap C should be opened to such an extent that the tempera- 
ture of the lower portion of the scrubber does not rise above 100 c 
Fahr. approx.. the top of the scrubber being cold. The amount 
by which the tap G is opened must be regulated according to the 
load on the engine and so that the evaporator is always full and a 
slight surplus of water runs in drops only through the overflow 
pipe T into the ashpit when the engine is running under a full 
load. When running under a light load little or no water is re- 
quired in the ashpit. An excess of water in the ashpit results 
in a poor quality of gas. 

4. To Start the Engine. — As soon as the gas is burning satisfac- 
torily at the test cock this cock and the cock J should be closed 
and the fan stopped. The engine should then be started hi the usual 
way. No time must be lost in getting the engine started or the fire 
in the producer will become dull and a poor quality of gas be given 
oft. Assuming that the engine has been started, the cock H should 
be opened and more water turned on to the scrubber by the tap C 
and to the evaporator by the tap G. The cock B should now be 
closed. By opening the cock H and closing B the air is drawn in 
through the inlet S and over the heated water in the evaporator 
F. the suction set up by the movement of the engine piston causing 
a constant indraught of air in the direction shown by the arrows hi 
the sectional diagram. It may be mentioned here that the supply 
of air to the engine will have to be adjusted from time to time 
according to the quality of the gas. For this purpose a simple 
form of throttle valve should be provided in the air inlet passage 
through which air is supplied to the engine. This valve should be 
regulated so that as far as possible the engine takes hi a supply of 
gas at every cycle and thus keeps the fire in the producer bright 
and hi good condition. The engine should be provided with 
mechanism to ensure this being done. 

5. Method of Stoking the Gas Producer. — The gas producer is 
provided with a hopper at the top for the purpose of feeding the 
fire. The hopper is provided with a swing door at the top and 
a valve with a weighted lever at the bottom so that when fresh coal 
is added the top door only is opened, the valve remaining closed. 
When the coal has been filled in through the hopper the top door 
is closed and the valve opened. By this means all air is excluded 
from the gas producer. Care should be taken to see that the valve 
to which the weighted lever is attached is properly closed so that 
no air can enter while the gas producer is working. Generally 
speaking it will be necessary to add a charge of anthracite every 
two or three hours ; this, however, must depend upon the size of 
the apparatus and the amount of power which the engine is develop- 



chap. vi| THE GAS PRODUCER 201 

ing. While the gas producer is in full operation the coal should 
not be allowed to fall below the lowest point in the evaporator. 
The to]) layer of coal should never be incandescent, this point can 
be watched through the mica window which is provided for that 
purpose at the top of the hopper. Previous to stopping the engine, 
however, the fire in the producer should be burnt down so as to 
leave only a moderate quantity of coal in the producer, sufficient 
to start up quickly again when required. How frequently the fire 
will have to be cleaned will depend upon the quality and amount 
of the fuel used ; speaking generally twice a day will be sufficient, 
once in the morning before starting and once at midday, if a stop- 
page is made then. Should it be necessary to stir up the fire whilst 
the engine is at work this can be done through a hole in the ash 
door by means of a poker. If it is necessary to take out the clinker 
whilst the engine is at work, this should be done very quickly so as 
to allow as little air as possible to enter the gas producer, for should 
an excess of air be allowed to enter, the gas would be of inferior 
quality. It is advisable as far as possible to leave the gas producer 
alone whilst the engine is at work, except for the occasional charges 
of coal which it requires. The gas producer should be cleaned out 
entirely about once a week and the clinker chipped off the firebrick 
lining of the producer if necessary. The producer should never 
be cleaned directly after the file is raked out, but should be allowed 
to cool down gradually, otherwise the firebrick lining will probably 
crack through the rapid change in temperature. 

6. Hydraulic Box. — The surplus from the coke scrubber is led 
into the hydraulic box W by means of the pipe D. This water 
forms at the same time a water seal for the pipe which connects 
with the separator mentioned above. The box W should be cleaned 
out every few weeks so as to keep it clear of the accumulated ash 
and small particles of coal which will come over with the gas. 
Special attention should be paid to the pipe D to see that no foreign 
matter settles in it. When the engine is at work the surface of the 
water in the hydraulic box will be in constant movement ; the 
movement, which should be a slight one, will vary with the amount 
of gas drawn away by the engine. An overflow pipe X is provided 
to run the water away from this box to a drain, or as may be 
arranged. 

7. Coke Scrubber. — -The coke scrubber is provided to remove 
from the gas all its impurities and at the same time to cool it. When 
the apparatus has been erected the inside of the scrubber should 
be thoroughly cleaned and the grating put in through the upper 
manhole. The scrubber should then be filled with well washed 
foundry coke, the size being not less than about 1 in. (25 mm.). 
The bottom layer of coke for a depth of about 8 in. (0 "2 m.) should 
consist of pieces which are under any circumstances so large that 
they will not fall through the grating. The scrubber can then be 



202 THE INTERNAL COMBUSTION ENGINE [chap. VI 

filled up with coke to about 4 in. (0*1 m.) below the water pipe. 
Before starting the bottom of the scrubber should be cleaned out 
through the doors provided for that purpose. All the openings 
in the scrubber should now be closed and the water supply turned 
on so that the coke is washed thoroughly free from all the particles 
of dust which it may contain. Every three or four weeks the 
bottom door of the coke scrubber should be opened to see whether 
there is any accumulation of dust in the form of mud at the bottom 
of the scrubber ; this if present should be removed. When the 
coke is first put into place this examination should be made more 
frequently, as new coke frequently contains a large quantity of 
dust. The coke in the scrubber will, generally speaking, be ser- 
viceable for a period of nine to twelve months, but this depends 
upon the amount of work which the plant has to do. When it 
is found necessary to renew the coke in the scrubber the whole 
of the apparatus must be stopped, the waste pipe opened and all 
the ash and fire hole doors opened and left open for several hours 
before any work is done to the plant. The upper cover of the 
scrubber should then be removed and the coke taken out through 
the upper side door in the scrubber. This cleaning should take 
place during the daytime so that no fire or light need be brought 
into the gas-plant house while it is going on. The windows of the 
house should be open during the process of cleaning so that there 
is plenty of ventilation. It is advisable that there should always 
be two men present during the operation of cleaning, in case one 
of them should be overcome by the presence of gas. When replac- 
ing the doors on the scrubber after having renewed the coke care 
must be taken to see that the joints are sound and tight as already 
described. 

8. Piping and Gas Box. — These should be looked to and cleaned 
about once a month. Impurities will settle in any pockets or where 
the course of the gas is not direct. For this reason all bent pipes 
should be avoided as far as possible and when present should be 
examined from time to time. The moisture which condenses in 
the gas box and in the pipe leading from it to the engine should be 
emptied out daily, otherwise it will get into the engine and interfere 
with its working. A drain cock should be provided, as at Y, for 
the purpose of drawing off this moisture. 

9. To Stop the Gas Producer. — The gas cock on the engine should 
be shut and the waste cock J opened so as to allow the remaining 
gas to escape. The taps C and G and the cock H must then be 
closed and the ash door opened a few inches so as to allow the fire 
to continue burning. 

10. To Start the Apparatus again after a Temporary Stoppage. — 
The fire and ash doors should be opened to clean the fire, any 
cinders or clinker should be removed without disturbing the fire 
as far as this is possible, the doors should then be closed, the cock 



(hap. vi I THE GAS PRODUCER 203 

B opened, and the fan started until the fire is again in good con- 
dition. Anthracite must then be added until a good quality of gas 
is obtained, when the engine may be started up to work. When 
the stoppage is only temporary, the scrubber and gas box will 
probably be full of good gas when it takes place, and it is there- 
fore better to test the fresh gas, made at restarting, by means of 
a test cock placed at Z rather than to test it at Q. When good 
gas is obtained at Z the cock J can be closed and the gas then sent 
through the scrubber and gas box to the engine. By following 
this plan the good gas remaining in the scrubber and gas box when 
the plant was stopped will be utilized, instead of being blown 
away to waste as might otherwise have been the case. 

Caution. — The regulation of the supply of water to the coke 
scrubber is important. If the supply be too small, steam will be 
formed in the scrubber, the gas will not be properly cleaned, and 
the quality of the gas will deteriorate. If the supply be too great, 
the water seal of the gas pipe will be too deep and the engine will 
not be able to suck the gas through the producer. The coal should 
not be too large or of unequal size, or the air spaces between the 
various pieces will be too great. The guiding principle in this is 
to have a mass of fuel in the producer which is as homogeneous as 
possible without being solid. Where coke is used as the fuel a 
sawdust scrubber is required between the coke scrubber and the 
gas box. When a gas plant has been designed for anthracite, other 
modifications may be necessary if it is decided to change from 
anthracite coal to coke. 



EXAMPLES 

1. The following measurements were made during a test of a gas 
engine using producer gas : Volume of gas used per hour = 1,400 cu. ft. 
Calorific value of gas = 90 C.H.U. per cu. ft. B.H.P. = 29-2. Water 
flowing through jackets = 70 gallons per hour. Rise in temperature 
of jacket water = 60° C. Calculate : 

(i) the number of C.H.U. supplied to the engine per hour, 
(ii) the number of C.H.U. turned into useful work per hour, 
(iii) the number of C.H.U. absorbed by the jacket water per 
hour. 

How much heat per hour is unaccounted for, and what has become 
of it ? 

2. A coal has the following analysis : carbon 88 per cent., hydrogen 
4 per cent., oxygen 2-4 percent., sulphur 1 per cent., the remainder 
being ash. Calculate the calorific value per lb. and the theoretical 



204 THE INTERNAL COMBUSTION ENGINE [chap, vi 

quantity of air required for its complete combustion. State how you 
would ascertain the quantity of air actually supplied. (Cal. values, 
C=8,130; H =29, 100; S =2,240.) 

(B. of E., 1912.) 

3. On a trial of a gas producer and engine the following particulars 
were noted : — 

Duration of trial, 24 hours. 

Total coal used, 2-4 tons. 

Calorific value of coal, 14,500 B.Th.U.'s per lb. 

I.H.P. of engine, 259^. 

Jacket-cooling water used per hour, 185 lb. 

Temperature of jacket-cooling water : — inlet 60° F. 

outlet 140° F. 

If the thermal efficiency of the producer is 80 per cent., and assum- 
ing no loss between producer and engine, estimate the thermal effi- 
ciency of the engine and the percentages of total heat of combustion 
lost : — 

(i) in the jacket-cooling water, 
(ii) in the exhaust gases, by radiation, etc. 

4. Suppose that for 1-2 lb. of coal we get 1 B.H.P.-hour from a gas 
engine using Dowson gas. This works a reversed heat engine, the 
mechanical efficiency of the engine being 85 per cent. Calculate the 
heat units added to the air per lb. of coal per hour and compare it 
with direct heating. What is the ratio of the amounts of air that can 
be heated over the same temperature range by the two processes. 
The calorific power of the coal is 8,200 C.H.IT. per lb. 



CHAPTER VII 

Blast-Furnace and Coke-Oven Gases 

Thermal Value — Cleaning the Gas — Utilization of the Surplus 

Power. 

126. The Production of Waste Power from Blast-Furnace 
and Coke-Oven Gases. — The plan of using blast-furnace and 
coke-oven waste gases in gas engines is now quite largely 
followed ; and the extent to which it may be put into force in 
any country depends chiefly upon that country's output of 
pig-iron. The following figures show the output in pig-iron 
in metric tons for the three countries chiefly concerned — 



U.S.A. . . 

Germany . 
Great Britain 



1911 



23,600,000 

15,300,000 

9,700,000 



The gas that issues from blast furnaces is rich in carbon- 
monoxide and poor in hydrogen, and has a calorific power of 
about 90 B.Th.U.* per cu. ft. : whereas the gas from coke 
ovens is extremely rich in hydrogen and may have a calorific 
value as high as 500 B.Th.U. f per cu. ft. The former is the 
easier to deal with as it is produced at a steadier rate, whilst 
with the small quantity of hydrogen which it contains, pre- 
ignitions are unlikely. Consequently it is safe to raise the 



* 50 pound-calories. 
f About 280 pound-calories. 
205 



206 THE INTERNAL COMBUSTION ENGINE [chap, vii 

compression to a much higher point (180 lb. per sq. inch or 
more) than would otherwise be safe, and the engine is thereby 
rendered of higher thermal efficiency. Both gases require 
cleaning in order to remove the dust. 

127. Blast-Furnace Gases. — The idea of burning blast- 
furnace gases directly in gas engines instead of under steam 
boilers, as had previously been done, was first put into practice 
about the year 1894. nearly simultaneously in Great Britain. 
Germany and Belgium. The pioneers, prominent among 
whom was the late Mr. B. H. Thwaite, experimented with 
small engines and, as satisfactory results were obtained, it 
was soon desired to increase the scale of operation. In Ger- 
many great progress has uoav been made and recently a number 
of large plants have been put in in this country and in the 
U.S.A. 

The calculation as to the power available in this way in 
Great Britain may be made in the following manner. The 
pig-iron output for 1911 (for example) was, in round figures, 

10,000,000 tons, 

and it is well established that the residual gases from blast 
furnaces in Great Britain as well as on the Continent and in 
America, are capable when used in internal combustion engines 
of yielding about 27 H.P. per ton of pig-iron per day (the figures 
given by various engineers are as follows : Greiner, 20 ; 
Bryan Donkin, 28 ; Max Rotter, 25 ; Thompson, 20 ; Rossi, 
30 to 35). It follows that the whole output would be about 

10,000,000 
365 

of which at present the greater part is going to waste. 

The corresponding H.P. for the 15,300,000 tons of output 
in Germany would be 1,100,000 H.P., which agrees generally 
with Dr. Hoffmann's estimate of 1,000,000 H.P. 

It is confidently calculated that in those countries where 
this development is in progress a saving of several shillings 
per ton will be made in the cost of producing iron. Several 
German firms, notably, have already found very favourable 
financial results to accrue. 



chap, vii] BLAST-FURNACE, ETC., GASES 



207 



Professor H. Hubert remarks * that in Belgium the honour 
of being first in the field belongs to Messrs. Bailly and Kraft, 
of the Cockerill Co. The patent taken out by the Company 
for this new application was dated May 15, 1895, and the 
first trials were made at the end of that year. They were 
made with a Simplex engine of 8 H.P., in which the clearance 
space had been reduced in order to increase the compression 
and to facilitate the ignition of the mixture. The gas cleaning 
was imperfect, and Avas carried out simply by passing it through 
two scrubbers four metres high. The engine is stated to 
have displayed . perfect elasticity, and adapted itself to the 
variations of composition, pressure and temperature of the 
gases. 

The following interesting table is taken from Professor 
Hubert's paper — 



Engine 



8 H.P. engine 

200 H.P. engine (single cylinder, 
single acting, constant ad- 
mission) 

600 H.P. engine (as above) 

200 H.P. engine (as above, ex- 
cept for variable admission). 

1,400 H.P. engine (double-acting 
tandem, variable admission). 



Date 

of 
Trials 


Power 


Calories 
used 


I.H.P. 
5-26 


B.H.P. 


I.H.P. 
Hour 


1896 


4 


4,030 


1898 


213-9 


181-82 


2,775 


1900 


825-8 


670-0 


2,520 


1901 


246-9 


215-3 


2,766 


1906 


1,755 


1,582 


2,129 



Ther- 
mal 
Effi- 
ciency 

per cent 
15-77 



22-9 

25-2 

23-0 

29-8 



128. Coke Oven Gases. — Coke-oven gases are much richer 
in hydrogen than blast-furnace gases, and they are therefore 
much more liable to pre- ignitions. To avoid this danger, the 
compression is not taken so high, although this precaution 
unfortunately has also the effect of tending to reduce efficiency. 
On the other hand their thermal value is far higher, often 
more than five times as high. To illustrate this, the following 
typical figures are given : — 



* Iron and Steel Institute, 1906, 



20S THE INTERNAL COMBUSTION ENGINE [chap, vii 

B.F. gas :— 24| per cent, of CO : 62 per cent, of N 2 ; 1} per 
cent, of H 2 ; Calorific value 86 B.Th.U.* per cu. ft. 
C. Oven gas : — 50 per cent, of H 2 ; 40 per cent, of CH 4 : 
Calorific value 560 B.Th.U. f per cu. ft. 
To calculate the possible output obtainable from coke- 
oven gases in this country is not difficult. Taking the 1906 
output of pig-iron as 10,000.000 tons, the consumption of hard 
coke may be put as about 11.000.000 tons. To produce 
this quantity of coke about 15,000,000 tons of coal would be 
required, which on coking would give off about one-fifth of its 
weight in the form of gas, corresponding to about 500,000,000 
cubic feet of gas per day. Assuming that a quarter of this 
is available as a surplus for use in gas engines, and that 
it is of the thermal value of 500 B.Th.U. t per cu. ft., the 
corresponding thermal energy is easily calculated. If the gas 
engines used have a thermal efficiency of 30 per cent., the 
following H.P. would be available : — 

i X 500,000.000 X 5Q ° X -^- X 0-30 = 306,000 H.P.,' 
24 X 60 33,000 

or in round figures 300,000 H.P. This is an estimate for the 
English output. Dr. Hoffmann has estimated the German 
output as from 550,000 to 600,000 H.P. Not a little enter- 
prise has been shown in Germany in harnessing this source 
of power, and action is being taken in this country to the 
same end. 

The proportion of one quarter, used in the above calcula- 
tion § as to the fraction of the gas available for the production 
of this surplus power, depends upon chemical problems, but 
it has recently been found that by raising the temperature 
of the air entering the ovens to 1.000 or 1.100° C. bv means 
of regenerators, only 45 to 55 per cent, of the total quantity 
of gas evolved from the fuel is required for the work of heat- 

* About 50 pound-calories. 

f About 330 pound-calories. 

£ About 380 pound-calories. 

§ ML Leon Greiner gives the following approximate rules for the 
amount of surplus power available for use : — (a) with blast furnaces, 
the continuously available H.P. is equal to the number of tons of iron 
made per month ; (6) with by-product recovery ovens, the continuously 
available H.P. is equal to the number of tons of coke made per week. 



chap, vii] BLAST-FURNACE, ETC., GASES 209 

ing the ovens, so that practically half the gas would in that 
case be available for the production of power in gas engines. 
This idea has been worked out by Mr. Koppers, and at the 
Anna Colliery of the Eschweiler Mining Co., near Aix-la- 
Chapelle, there are reported to be six batteries of Koppers 
regenerator ovens, with a power station designed for the 
production of 16,000 H.P. from the surplus gas. 

It is on record * that at the Wath Main Colliery, Wath- 
upon-Dearne, Rotherham, an installation of 30 Huessener 
patent by-product coke ovens, erected by the Coal Distillation 
Co. of Middlesbrough — representing the Actien Gesellschaft 
fuer Kohlendestillation — has been put in. The plant is to 
produce 800 tons of blast-furnace coke per week, and there 
is to be available sufficient surplus gas and surplus waste 
heat to produce 300 H.P. of electricity from the 30 ovens, 
in addition to meeting the requirements for power for coal 
grinding, elevating, and by-product plants. There are other 
instances of similar enterprise whereby English firms, on 
discarding the old " beehive " type of oven, have been able to 
obtain large quantities of surplus power. Of course there are 
other by-products besides power produced from coke ovens, 
such as sulphate of ammonia, coal-tar and benzole. 

129. The Shelton Iron Works have some Koerting Engines 
working on coke- oven gases, and it has been found f that when 
some coals are used a calorific value of over 600 B.Th.U.J 
per cu. ft. is obtained, although 400 is more common. In no 
case, however, is the quality constant during the whole period 
of coking. It usually decreases from about 450 to 350 during 
the operation. The gas passes through scrubbers, where the 
ammonium sulphate and other by-products are collected and 
most of the tar removed. The gas then is divided into two 
almost equal parts, one half going to heat the coke ovens, and 
the rest to the production of power. As the gas contains much 
hydrogen, naphthalene, and other highly inflammable bodies, 
it is liable to pre-ignitions, and the compression is kept down 
to 100 lb. per sq. inch, instead of the 140 lb. per sq. inch, which 

* Times E.S., April 17, 1907. 

t Engineering, February 15, 1907. 

% About 330 pound-calories. 




210 THE INTERNAL COMBUSTION ENGINE [chap, vii 

would otherwise be customary. The mean pressure works out 
at about 75 lb. per sq. inch. On testing a new variety of fuel 
the following results were obtained : Thermal value of gas 
381 B.Th.U.* per cu. ft., engines developed 1 H.P. per hour per 

22 cu. ft. at full load, or a thermal efficiencv of 



22 X 381 X 7> 



•30. The analysis of the gas was— 




co a 


3-55 per cent 


Olefines. etc. 


5-18 „ 





l-o9 ,, 


Methane . 


27-82 .. 


H> 


54-33 .. 


N a 


316 .. .. 



According to some figures in The Engineer, of 22 installations 
in Germany with a total output of 13.000 H.P. from engines 
working on coke-oven gas. no less than eleven, or half of them, 
do not find it necessary to clean the gas. One of them was 
stated to be using gas with 0-2 per cent, of sulphur without 
injurious effect on the iron. 

130. Cleaning' the Gas. — It has been found that the most 
effective way of cleaning the gas is by the action of a wattr 
fed fan. The gas passes through a centrifi gal fan which 
causes the heavy particles of dust to fiy outwards, and at the 
same time water is fed into the fan and broken up by the 
same centrifugal action. This water catches up the dust 
particles and passes with them to a sump. Perhaps the best 
known gas cleaner of this type is the Theisen Patent Cen- 
trifugal Central-flow Gas Washer, made by Messrs. Richard- 
sons. Westgarth & Co. It is illustrated in Figs. 61 and 62. 
The Theisen machines are specially adapted for cleaning gas, 
and particularly blast-furnace gas, for use in gas engines and 
where a high degree of purity is required. When very hot 
and dirty gas has to be treated, it is considered advisable 
to instal a preliminary saturator before the washer, where 
the gas may be cooled and the heavier dust removed. In 
this way not only is the volume of gas to be cleaned reduced, 

* 212 pound- calories. 



chap x u] BLAST-FURNACE, ETC., GASES 



211 



Gas Inlet 




Fig. 61. — Theisen Gas Washer — Section. 



Gas Outlet 



Water 
Inlet 



but less water is required in the washer itself, and conse- 
quently less power is absorbed. The makers claim that the 
power taken to drive the cleaner does not exceed 2 per cent, 
of the maximum power which could be generated in gas 
engines from the gas cleaned. The quantity of water required 
by the Theisen 
apparatus varies 
with the tempera- 
ture of the gas 
and the amount of 
dust therein, and 
in addition with 
the degree of 
cleaning n e c e s- 
sary. With hot 
and dirty gas it 
sometimes hap- 
pens that as much 
as 1 litre of water 
is required per 

cubic metre (or 1 ,000 litres) of gas cleaned, but usually half this 
quantity will suffice. Of course the water can be used again 
and again, if the dust be allowed to settle out of it. The makers 
have published the following table showing results of trials : — 




CulvertJ 
Fig. 62. — Theisen Gas Washer- 



-End Elevation. 




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chap, vii] BLAST-FURNACE, ETC., OASES 213 

The amount of dust in the gas can be measured very easily. 
It is only necessary to pass the gas through a filter consisting 
of a glass tube rilled with absorbent cotton. The quantity 
of gas passed is measured in a meter, and the cotton is weighed 
before and after. The method is stated to give accurate 
results if the cotton is evenly packed along the tube and is not 
hygroscopic. In any case the cotton should be dried before 
and after in a desiccator, and weighed from time to time to 
check whether any moisture is held in it. 

In America,* peculiar difficulties are experienced, owing to 
the character of the ores used. The Mesati ores are stated to 
be especially troublesome, owing to their friable nature. With 
every disturbance in the furnace great quantities of dust are 
evolved, which often pass the entire cleaning plant unless 
unusual precautions are taken. The suspended matter consists 
largely of ore dust together with some additional matter 
carried over from the other constituents of the furnace charge. 
At Bessemer, however, a cleaning plant has been put down 
which has cleaned the gas as low as 0-1 grain per cubic foot, 
which is considerably cleaner than the surrounding air in 
that particular locality. In practice, however, the engines 
work quite well with ten times this amount of dust. 

131. Utilization of Surplus Power . — The utilization of the 
power derivable from the waste gases of blast furnaces and 
coke ovens is a problem in itself. The solution of this problem 
must depend upon the extent to which local demand for 
power exists, or can be created. It is only necessary to think 
of such electro- metallurgical processes as the manufacture 
of aluminium to bring to mind the possibility of the creation 
of huge demands for current under favourable conditions 
in respect of load factor. For the transmission of such 
power for any distance less than half a dozen miles, it would 
probably be most economical to use pipe lines to convey 
the gases, but for longer distances electrical transmission 
would be the obvious method to adopt. Another industry 
that might be served is the manufacture of calcium carbide. 
Carbide is not now being manufactured in bulk in this country, 
owing to the lack of cheap power. Abroad, engineers have 
* Times E.S., July 17, 1907. 




214 THE INTERNAL COMBUSTION ENGINE [chap, vn 

the advantage of extraordinary cheap water power — as low, 
according to Professor S. P. Thompson, as J (T part of a penny 
per H. P. -hour — and it is clear therefore that unless some 
very cheap source of power is rendered available here also it 
will not be possible for this country to produce its own 
carbide. Calcium carbide, in its purest form, is used for 
the production of acetylene for lighting purposes, but a 
less pure and cheaper kind can be used in the preparation of 
chemical manure, for which the demand is on an altogether 
larger scale. 

Lime and coke when heated together to a temperature of 
2,000—3,000° C. produce calcium carbide, combining in 
accordance with the following chemical formula — 

CaO + 3C = CaC 2 + CO. 

This reaction is carried out in an electric furnace worked 
either by direct or alternating current, although as the latter 
allows of a higher voltage transmission and simple trans- 1 
formation, it is usually preferred. It is a high temper at ure 
reaction and not an electrolytic one, thus permitting either 
type of current to be used. In the above equation the CO 
passes away as a by-product, and carries with it one-third 
of the carbon used. This gas might of course be collected 
and its thermal value used say for the heating up of the 
charge of lime and coke, for the earlier part of the great 
temperature range necessary. The amount of current needed 
to produce 1 ton of calcium carbide is about -J H. P. -year. 
Mr. Bertram Blount in his Practical Electro-Chemistry remarks : 
— " The surplus gas (from coke ovens and blast furnaces) 
can be used with economy in large gas engines of 500 or 1,000 
H.P., and energy thus obtained almost as cheaply as from a 
water-power. Eor example, at an inclusive cost of Y T) d. per 
H. P. -hour, which is by no means unattainable, the price per 
H. P. -year is £3 13s., a figure which approaches that of a 
moderately cheap water-power. The real obstacle to the 
general utilization of such power is not its cost, but the some- 
what restricted market for carbide, causing it to be readily 
swamped by any great increase of supply ; even with that 
restriction, however, the manufacturer having cheap coke 



chap, vn] BLAST-FURNACE, ETC., GASES 21 

and lime in an industrial centre, will stand at least as good a 
chance as his rival with slightly cheaper power, but away from 
such supplies." 

132. Owing to the discovery that calcium carbide could 
be used in the preparation of an excellent chemical manure, 
the possibility has been opened up of an enormous demand 
for this product, thus affording a suitable purpose to which 
large quantities of electric power could well be devoted. Such 
an enlargement of the calcium carbide market might not be 
altogether welcome to present manufacturers of the carbide, 
as the new product, not being used in the production of acety- 
lene gas for lighting need not be so pure. A heavy demand 
for the less pure carbide might therefore lead to difficulty in 
obtaining small supplies of a purer kind, as it would hardly 
be worth while undertaking it. Or even if undertaken, the 
cost of such carbide might actually be greater with the increase 
of output than it is now. Probably if the bulk of the output 
were of a different quality it would not be feasible commercially 
to produce raw carbide in so pure a state, but this would not 
prevent the impurer carbide being purified by subsequent 
treatment in such quantities as the acetylene demand might 
necessitate. Even if chemical difficulties present themselves 
in the purification of the carbide when made, there is no reason 
to suppose that the ingenuity of chemists will be unable to 
circumvent those obstacles as soon as it is necessary for them 
to be dealt with. Present-day manufacturers hold to preven- 
tion being better than cure, and would far rather see that 
purer raw materials (coke and lime) were used ; but if a big 
agricultural demand should arise, it is not to be expected that 
subsequent modes of manufacture would be controlled entirely 
with a view to the smaller market. The virtue of calcium 
carbide from the agricultural point of view lies in the fact 
that it can be converted into calcium cyanamide, which can be 
directly applied to land as a fertilizer, and that when so employed 
it is of great value and efficacy. The cyanamide can be ob- 
tained direct from the carbide by fusing the latter in a stream 
of nitrogen. Or if preferred, the process may be shortened 
by admitting nitrogen to the electric furnace in which the 
lime and coke are being fused. 



216 THE INTERNAL COMBUSTION ENGINE [chap, vii 

EXAMPLES 

1. A gas engine indicates 60 H.P. when using gas at the rate of 800 
cu. ft. per hour. The calorific value of the gas is 300 C.H.U. per 
cu. ft. Calculate the thermal efficiency of the engine. 

(B. of E., 1912.) 

2. The following data are taken from a record of a test of a gas 
engine using power-gas : — -cylinder diameter = 48 in., stroke = 54 
in.. M.E.P. = 75 lb. per sq. inch. Xumber of explosions per min. = 
36. Gas used per min. = 1020 cu. ft. Calorific value of gas = 60 
C.H.U. per cu. ft. B.H.P. = 545. Calculate :— 

(i) The I.H.P. 

(ii) The mechanical efficiency of engine, 
(hi) Volume of gas used per I. H.P. -hour, 
(iv) Volume of gas used per B.H.P. -hour. 

(v) Indicated thermal efficiency, 
(vi) Brake-thermal efficiency. 



SECTION III 
iND PETROL ENGINES 



CHAPTER VIII 

Oil and Petrol Engines 

Fuels — Slow-Speed Oil Engines — Diesel Engine — Petrol 
Engines for Motor Cars and Aircraft — Carburettors — 
Theory of Jet Carburettors — Ignition. 

133. Fuels. — Internal combustion engines are of two classes : 
(1) those that work with gases for their explosive medium, 
and (2) those that use vapours of liquid hydrocarbons such 
as oils. The former class has been dealt with in the preceding 
chapters so far as everything except methods of ignition is 
concerned — and ignition being similar in both classes does 
not need to be dealt with in two parts. Oil and petrol engines, 
as those in class (2) are generally named, are of practically the 
same design as gas engines so far as cylinders, pistons, valves, 
etc., are concerned, and the difference between them mainly 
relates to the mechanism for dealing with the fuel used. A gas 
engine does not need any carburettor, whereas in the oil or 
petrol engine it is one of the most important and most sensi- 
tive parts. 

The main requirements of liquid fuels for internal combus- 
tion engines are that they should 

(1) Be moderate in cost ; 

(2) Be free from anything which might lead to deposit 

inside cylinders ; 

(3) Cause a minimum of difficulty when starting the engine ; 

(4) Not lead to objectionable exhaust. 

The liquid fuels in common use are heavy or medium oils, 
petrol, alcohol, and certain coal-tar products. 

The crude petroleum coming from the well is treated at the 
oil refiners in such a way as to separate the light constituents 
from the heavy. This process is known as " distillation." 

219 



**M 



ixtessal come ^ ::/ :; I 



--- - - -- :~ .- -: --7 \^ --'. ... Lvrr- -.- :T ^--' ; V- -^ ; ^; ; 

and as the Tapoms are grreni ©ffi they are led to a separati 
chamber and these condensed into fractions a 
boiling paint or density. 

... i :L~ = __:_ : ■ . ■ - ■ ■ - : i - . . T — '. 



tons. This total is very small i 

- : : ' . ~'zl:'z > zizrr "_" - :_ 
extensive new supplies of oil 

-"-•-:: : : :-~ \ .- s : '_ i :j 1:: 

7it - : :m : t- : : :._r --:- 1L7 :: -:■--;: 
r .~i>: .2, 

I ~ '■''" ~~ ~~- 
-. ::__-::_:: . 

- "• '_ : : i 
Iz :;_ .:. 
"„tI : : - — -^> 



he well is abont®-$ to 0-9, 

r— :r-ii/- i~ : ~: ":•: »; X»0 
: : ii: -.:^ ■:". — t1 "_- : \:~.- -;- 
nes as great), and unless 

-- . _ tI^ '. :: :- :: t.t— :•: 

i in 1 . - — t : - — : : '_ ; — = — 
. 1$-© per cent. 

. 3-7 

- - 

2-3 

. 2-1 

- 



: :•: " 

I: — _ t :r-7_ -_-: :1t r.:- - — : ::::::-::-- _::■" ;:-:! ». 
per cent, of the whdle. 

Pemisvlvanian petroleum consists of a mixture* of hydro- 
carbons of the CJBLj^^ group in "which m may be anything 
from 1 to, say, SQL and the baihng paint rises gradually from 
©"CI for C1H M to 280* C for C m U^ Hexane (CAJ, which 
liasabailingpoiiitof 6S^C. and a density of €MS@7. Is practically 
a light petrol : but the heavier petrols come neater to octane 
(CJffJ, which bons at 125° €. and has a density of 0-718. 
1:34.. ?t~T':'.. — 'z-rz '_* :.il>i ^-:L:..t iT ; A Li :z.~ :: 
:ir :i-';";tI"- " :' " - _ : _- ":__ ' ::*: : : i___t:'::a. 
s to distil at 30= C. : at StTC.to SOPCL about 5G>% 
. . " ~_t "._t "„t ~7_~ ■■t:-." :':j-t - .". ; .'T-ri :■•;-..": 
it has been separated. This temperature range 
Centigrade and is called the " distillation range. 77 
cceHent fuel for motor-cars, having all the desar- 

~'r ~-Z L'~~ ''■ I-"*'";'.- ~ ' 



: i_t ; : ~-: 

i5trc.an 




CHAP, vni] OIL AND PETROL ENGINES 221 

able characteristics. In 1902 the quantity imported into the 
United Kingdom was less than 6,000,000 galls. ; in 1913 it 
was over 100,000,000 galls. 

In the early days of motoring petrol was, usually of about 
0-68 specific gravity. Now, however, it is nearer 0-74. The 
best quality of petrol has a specific gravity of from 0-715 to 
0-730 and yields 63 per cent, on distillation at 100° C. and 
90 per cent, at 120° C. The calorific value is 10,800 pound- 
calories (19,500 B.Th.U.) per lb. (This is the " net " calorific 
value, as it does not include the latent heat of condensation 
of the water vapour formed by combustion.) 

As is indicated by the large distillation range, petrol is not 
a single homogeneous product ; but its average composition 
corresponds fairly closely to the chemical formula C 8 H 18 . 

135. Paraffin. — Paraffin (called " Kerosene " in U.S.A.) is 
the next constituent to distil over. Its distillation range is 
much greater than that of petrol, being from 100° to 300° C. 
It is therefore even less of a homogeneous product than is 
petrol, and it is, moreover, not possible to draw a distinct line 
between the two, the one merging into the other. The specific 
gravity of paraffin is about 0-81. Its calorific value (net) is 
12,500 pound-calories (22,500 B.Th.U.) per lb. Its average 
composition corresponds to C 10 H 22 - Owing to its large dis- 
tillation range carburation is more difficult than with petrol, and 
it is seldom used therefore for engines of the motor-car type. 
After the paraffin has distilled over the remainder is separated 
into lubricating oil, residual oil, vaseline and paraffin wax. 

136. Benzol. — The coal-tar product which is found to be 
suitable for use in internal combustion engines is benzol. 
It is a colourless liquid having a specific gravity as high as 0-88. 
The approximate chemical formula is C 6 H 6 * and its calorific 
value is about 11,000 pound-calories (19,800 B.Th.U.) per lb. 
It begins to distil at 80° C. and ends distillation at 120° C, 
showing that it is a more nearly homogeneous product than 
either petrol or paraffin. Owing to its high specific gravity it 
has a much higher calorific value per gallon than petrol. Its 
volatility renders it quite suitable for use in motor-cars, and 

* "Benzene," the chief constituent of benzol; another — less im- 
portant — constituent is toluene, C 7 H S . 



222 THE INTERNAL COMBUSTION ENGINE [chap, viii 

it can be employed without any changes whatsoever in engine 
or carburettor. Some qualities have the disadvantage that 
at 0° C. they freeze solid, but the presence of a proportion 
of toluene in the benzol removes this difficulty. 

137. Alcohol. — Alcohol is a volatile and colourless liquid of 
vegetable origin with a chemical formula of C 2 H 6 0. * Its specific 
gravity is 0-80. It distils completely between 80° C. and 
100° C.j and the calorific value is 7,000 pound-calories (12.600 
B.Th.U.) per lb. It is, however, little used for fuel in England 
owing to the high Government duty. 

Efforts have been made to encourage the use of alcohol in 
internal combustion engines, because of the cheap rate at 
which it can be manufactured on a large scale and because 
if produced here this country would be rendered independent 
of supplies of motor fuel from overseas. 

138. Tabular Statement. — It is convenient to summarise 
the more important data in the form of a table 



Liquid Fuels 



Substance 


Specific 

gravitv 

at 15° C. 


Distillation 

range 
cleg. Cent. 


Calorific 
value (net) 

C.H.U. 
per pound 


Calorific 

value 

C.H.U. 

per Imperial 

gallon 


Approximate 

Calorific 

value in 

ft. -lb. per 

pound 


Paraffin . 


0-81 


100/300 


12,500 


102,000 


18,000,000 


(C 10 H 22 ) 
Petrol 


0-73 


50/150 


10,800 


79,000 


15,000,000 


(C 8 H 18 ) 
Alcohol 


0-80 


80 100 


7,000 


56,000 


10,000,000 


(Co H 6 O) 
Benzol 


0-88 


80 120 


11,000 


97,000 


15,000,000 


(C 6 H 6 ) 













139. Alcohol and Benzol Compared with Petrol.— The 
Fuels Committee of the Motor Union in their 1907 Report 
dealt largely with this matter. The following extracts are 
given — 

" (1) Safety. — In the first place, in case of possible conflagra- 
tion, alcohol can be extinguished by water, whereas petrol is 
only scattered under similar circumstances, and the area of 
* Known chemically as Ethyl Alcohol. 




chap, vinj OIL AND PETROL ENGINES 223 

conflagration increased. In the second place, and even more 
important, the flash point is considerably higher, being 60° 
Cent, compared with petrol, which may be taken as anything 
down to 10° Cent, below freezing point. This enables the 
alcohol to be carried and stored with safety under conditions 
where petrol would not be permitted. This further very much 
reduces the cost of freight and insurance. 

" (2) Thermal Efficiency. — Owing to less air being required 
and a consequent reduction in the amount of inert gas, the 
thermal efficiency of alcohol is as high as 35 per cent., as against 
something below 20 per cent, in the case of petrol, and this 
greatly reduces the chances of overheating, besides also reduc- 
ing the weight of cooling water, radiator, etc. 

' (3) Calorific Value. — The calorific value of absolute 
alcohol is 12,600 B.Th.U., that of methyl alcohol with a specific 
gravity of 0-820 is 11,300, and alcohol with the addition of 20 
per cent, of water shows a calorific value of 9,810 ; whereas 
that of petrol with a specific gravity of 0-722 ranges from 
20,300 to 19,300 B.Th.U. 

' (4) Practical Limit of Compression. — The practical limit of 
compression of alcohol is about 200 lb. per square inch ; and 
its explosion pressure is therefore considerably higher than 
that of petrol, the practical limit of compression of which — 
in view of possible pre-ignition — is limited to 80 lb. per square 
inch. 

' (5) Complete Combustion. — With alcohol complete com- 
bustion is more easily attained, owing to the fact that it 
distils completely in its commercial form over a small range 
of temperature (80-100° Cent.), a very accurate degree of 
carburation thus being maintained. In the case of petrol the 
range of boiling point extends between 50° Cent, and 150° 
Cent. ; such a large range of boiling points renders accurate 
carburation at all times more difficult, and makes the spirit 
what is commonly known as stale owing to the evaporation 
of the lighter fractions. Alcohol has not this disadvantage, 
the liquid being practically homogeneous throughout. 

' (6) Propagation of Flame.- — There is less rapid propagation 
of the flame when alcohol is used, which gives a much more 
uniform pressure throughout the stroke than petrol. 



224 THE INTERNAL COMBUSTION ENGINE [chap, yiii 

' (7) Smell. — With alcohol there is approximately no 
offensive smell in the exhaust, as compared with petrol. 

"' (8) Flexibility.- — Alcohol will explode when mixed with 
air over a wider range than petrol — i— 13 per cent, alcohol 
vaponr in air being combustible, the range in the case of petrol 
vapour being 2-5 per cent. ; thus the engine will be much more 
flexible. * 

'•' There are three points, however, on which it is popularly 
supposed that alcohol compares unfavourably with petrol. 
These are : 

(9) Corrosive effect 

(10) Starting from cold 

(11) Vaporization. 

'"' (9) Corrosive Effect. — With regard to alcohol., any corro- 
sive effect that may occur is probably due to impurities in the 
denaturing agent present in acetone and methyl alcohol., but 
these difficulties would be overcome if the carburation is such 
as to give complete combustion. Upon this point Dr. W. R. 
Ormandy writes to the Committee as follows : 

' My information with regard to the action of the effluent 
gases from motors running on alcohol was obtained from the 
engineer at the Gahrungsversuchsanstallt at Berlin, who 
reported that engines running on pure alcohol, or even on pure 
alcohol with the German denaturant. gave no appreciable 
corrosion excejDt on such parts of the motors as were so cold 
that condensation took place : thus the silencer was apt to 
corrode, more so the larger the percentage of water in the 
alcohol employed. As the average amount of water at present 
in German industrial alcohol is 10 per cent... this corrosion 
might become appreciable if the cooling of the cylinder walls 
was too effective. It has been proved, however, that the 
efficiency of alcohol engines is enormously increased by keeping 
the cylinder walls near the temperature of boiling water, and 
under these conditions no condensation and no corrosion 
obtained.' 

"' (10) Starting from Cold. — As for difficulty in starting from 
cold, it will be probable that alcohol as a fuel will almost always 
have a greater or less quantity of benzol mixed with it, in which 
* This is more accurately explained in par. 142. 



(hap. vin] OIL AND PETROL ENGINES 225 

case this difficulty entirely disappears. Even without the 
addition of benzol there is little doubt that the question of 
starting from cold will be almost entirely overcome by the 
use of a suitable carburettor. 

"(11) Vaporization. — Alcohol requires 5 J per cent, of its 
total heat of combustion to vaporize it, whereas, on the other 
hand, petrol vaporizes without any external assistance. With 
regard to the heat required to vaporize it, it is to be noted that, 
inasmuch as a large amount of the heat produced passes off 
in the exhaust, this is really available for the purpose of 
vaporization and does not represent any thermal loss. 

" Other Means of Utilizing Alcohol.- — From the previous 
argument it will be seen that, in order to utilize alcohol in an 
internal combustion engine, certain modifications in the 
engine itself become necessary, but it is quite reasonable to 
expect that such alterations would be unnecessary if the 
proportion of tar benzol, acetylene, or other hydrocarbons 
containing a high percentage of carbon were mixed with the 
alcohol. Owing to this high percentage of carbon present, 
the chemical composition of the mixture will be brought more 
nearly to resemble that of the petroleum products. As to 
the most suitable relative proportions, experiment only will 
determine these, but such a fuel as is here suggested has the 
advantage of being a home production, as well as one that 
could be used without material alteration to the engine. 

: ' It has been stated in evidence that the average price at 
which alcohol can be produced in Germany amounts to Is. a 
gallon, including the cost of denaturing and Government 
supervision. It is also a fact that in this country the actual 
cost of manufacturing alcohol amounts to HJcZ. a gallon (64 
overproof , a strength common in industrial spirit) — see Report 
of Departmental Committee on Industrial Alcohol. This is 
produced from beet, potatoes, and molasses. Evidence has 
been given which tends to show that alcohol may also be 
produced from sawdust at a very low cost. The lowest figure 
it is possible to touch in this respect is 3d. per gallon when peat 
is used. Now, owing to the great strictness of the Excise 
authorities in England, the cost of denaturing and expenses 

Q 




226 THE INTERNAL COMBUSTION ENGINE [chap, viii 

of supervision bring the total cost of the alcohol up to about 2s. 
per gallon at the present time, and it is therefore evident t hat- 
should the Government see their way to take a wider view of the 
question of alcohol as a fuel for internal combustion engines 
this price of 2s. a gallon could be very materially reduced. If 
this were done, the price could easily be brought to such a 
figure that it would be a very serious competitor with petrol 
in this respect alone. 

: ' The Government that will recognize this, and will allow 
untaxed alcohol suitably denatured to be used for light, heat, 
or power, will be conferring an immense boon and benefiting 
a very large proportion of the population." 

As regards the use of benzol the Committee remark : 
' What is commonly known as 90 per cent, benzol can be 
utilized with perfect success in the engine of a motor car either 
alone or mixed with petrol, or mixed with alcohol. Owing to 
the high percentage of carbon which is found in benzol, and to 
the low percentage of carbon in alcohol, it is evident that a 
mixture of these two liquids more nearly approaches the 
ordinary hydrocarbon liquid fuels to which we are accustomed 
in its chemical composition. Benzol will carburate air in the 
ordinary way when an ordinary petrol carburettor is used, 
but its specific gravity is very much higher than that of petrol, 
viz. 0-883, which may necessitate an adjustment of the float 
to prevent the benzol standing too low in the jet of the car- 
burettor. Crude benzol inevitably contains a certain amount 
of foreign matter in combination with sulphur, which imparts 
to it an unpleasant smell in the liquid state. Owing to its 
comparatively low price, however, it might pay to have benzol 
still further treated after washing in order to remove these 
impurities, which could be done for the expense of about Id. 
per gallon. At the present time benzol cannot be obtained 
in very large quantities, as the number of recovery plants in 
this country is not very large. As benzol is a home production, 
its use should be encouraged, and particularly at this present 
time when the difference between the prices of petrol and benzol 
is very small. 

" Mixtures of benzol and alcohol have been tried in a desul- 
tory manner on the Continent, but in this country nothing has 



chap, viii] OIL AND PETROL ENGINES 227 

been done upon an extensive scale. The possibilities for the 
successful use of such a mixture are very great, and both these 
fuels are capable of manufacture in this country in very large 
quantities. Although a mixture of benzol and alcohol is in 
its normal state quite nauseous, and would not require a further 
treatment such as the addition of wood naphtha, yet it is 
possible, at any rate, to partially separate these two liquids, 
the alcohol having an affinity for water." 

140. Sources of Petrol Supply. — The advent of the motor 
car has been the main cause of the increase in the demand 
for petrol, which previously had been regarded as a waste 
product. Petrol is now one of the most valuable components 
of crude mineral oil. According to Boverton Redwood and 
V. B. Lewes * the following are the leading sources of the 
petroleum spirit (or petrol) imported into Great Britain :— 




United States 

Sumatra, East Indies, Borneo and Netherlands 

Russia and Rumania 

Other Countries 



20 
57 
11 
12 

100 



Processes have been tried and are to some extent in use in 
this country, for obtaining petrol from paraffin or heavier 
oils by the chemical process known as " cracking." There is 
a tendency, however for these processes to be kept secret. 

141. Latent Heat of Vaporization of Liquid Fuels.— When 
water is raised to the boiling point and the application of heat 
is continued, some of the water is converted into steam ; each 
pound weight of water formed into steam at 100° C. needs 
537 pound-calories to effect the conversion. This 537 calories 
is called the latent heat of vaporization of water, or sometimes 
the latent heat of steam. In the same way, heat has to be 
given to petrol, paraffin, benzol, or alcohol to vaporize them. 
When these fuels are being used in internal combustion engines 

* Imperial Motor Transport Council, 1913. 



22- THE INTERNAL COMBUSTIOK ENGINE "chap, vm 



they need to be vaporized, and the heat necessary for vaporiza- 
tion is drawn from the air and metal in contact with them. 
If this heat be not provided in some way the fuel in the car- 
burettor will get so cold that it will not vaporize satisfactorily. 
The usual way of maintaining the temperature at a satisfactory 
level is either to warm the entering: air by making it pass 
round the hot exhaust pipes, or by jacketing the carburettor 
with cylinder- jacket water. If the former plan be followed 
it is found that the air needs to be heated by the following 
amounts for the f ueLs mentioned : — 

Petrol .... about 25 : C. 77 : E. 



zol 
Paraffin 
Alcohol 



30° C. (86° F.) 

: u«> : e. 

100° C 212 F.) 
142. Proportion of Air to Fuel. — The chemical composition 
of petrol varies with its density, but taking it at the average 
of QjH M3 the equation for complete combustion with oxygen is 

2Q I H 11I +250 2 =16C0 2 +18 H 2 
showing that 1 volume of petrol vapour will need for its com- 
plete combustion 12| volumes of oxygen. And since air 
contains 2 3 per cent, of oxygen by weight, or 21 per cent, by 
volume, each volume of petrol vapour will need about 60 
volumes of air. It is also possible to calculate the proportion 
by weight instead of volume. Thus in the above instance 
2 96 -\- 18) pounds of petrol need 25 X 32 pounds of oxygen 

pounds of air. 



and therefore 



. 



The number of 



pounds of air needed for the complete combustion of one 
pound of petrol is therefore — = 15 pounds. 





Proportion of Air to Fuel for complete combustion 


:-;r. 




-■'-■'-' '"'' ■'-'■- ' 


Paraffin 

Alcohol 

Benzol 

Petrol 


u 

14 

- 
60 


15 

9 

13 

15 



jhap. viii] OIL AND PETROL ENGINES 



229 



The foregoing table gives also the corresponding figures for 
paraffin, alcohol and benzol. These are the proportions for 
complete combustion, but proportions varying within limits 
from these ideal figures will also explode. This is shown in 
the following table : — 





Ratio by volume to air 


Substance 


Ideal 


Practically possible 


Alcohol. 

Benzol .... 

Petrol .... 


7 per cent. 

« 55 55 

17 „ 


40 per cent, to 13-6 per cent. 

«" ' 55 55 55 t>"0 ,, ,, 
I'O 55 55 55 *>'0 55 55 



143. Calorific Value of Explosive Mixtures. — Although the 
calorific values of fuels vary so much — thus the calorific value 
of illuminating gas is many times as great as that of blast 
furnace gas — there is relatively little difference between the 
calorific volumes of the explosive mixtures formed with them. 
This is because the rich fuels are diluted with a great deal of 
air, and the poor ones with very little. The following table 
illustrates this : — 



Fuel 



Blast-furnace gas 
Producer gas 
Coke-oven gas . 
Illuminating gas 
Alcohol vapour 
Benzol vapour . 
Petrol vapour . 
Paraffin vapour. 



Approx. calorific 
value per cu. ft. 



pound-calorie. ; 

50 

70 ' 

30) 

350 

900 

2390 

3420 

4960 



Volumes of air 

theoretically 

needed for 

combustion 



0-6 

0-9 

5 

5 
14 
32 
60 
74 



Approx. calorific 

value per cu. ft. 

of mixture 



pound- calories 
31 
37 
50 
58 
60 
72 
56 
66 



In practice there is always present some excess of air over 
and above the amount theoretically needed ; this leads to a 
reduction in the average calorific value of the gaseous mixture 



230 THE INTERNAL COMBUSTION ENGINE [chap, viii 

and probably brings the figures in the last column of the 
above table still nearer to one another. 

144. Slow-speed Oil Engines. — As an ordinary petrol engine 
which is run on paraffin becomes thereby an " oil engine," 
it is necessary to bring in the variable factor, speed, in order 
to distinguish it from the older and heavier types of oil engine. 
The former runs at, say, 1,000 revolutions per minute and over, 
and the latter at only a few hundred. Neither is essentially 
different from the other. If a petrol engine is imagined as 
greatly increased in size — say to a cylinder diameter of 14 in, 
— and all parts increased in proportion, the safe speed at 
which the engine will run will need to be reduced, because 
whilst the weight of moving parts goes up with the cube of the 
dimensions, sectional areas of stressed metal only increase as 
the square. It is not possible therefore to aim at high speeds 
without greatly increasing the cost of production. The build- 
ing of such expensive engines is frankly put on one side and 
a cheap engine is built which will run at a very slow speed, , 
slower even than the proportion to the increase in dimensions 
would naturally suggest. This enables cheaper materials to 
be used than are employed in the construction of petrol engines. ■ 
The output in horse-power is reduced in proportion to the 
speed, but increased as the cube of the cylinder dimension 
provided that ports, etc., are designed of sufficient size to 
enable the working mixture to enter and leave the cylinder 
without undue obstruction. 

As representative of this heavier class of engine the well- 
known Campbell oil engine is selected. 

145. The Campbell Oil Engine is illustrated in Figs. 63 
and 64. Fig. 63 shows the engine to be somewhat similar 
in plan to a horizontal gas engine and the engine parts are 
generally on that scale. The inlet valve C and exhaust valve 
G are shown in position. The latter is worked through a lever 
H and side rod J by an eccentric K driven from the crank- 
shaft L by spur gearing. When the speed exceeds the normal, 
a centrifugal governor pushes down a steel piece N, which 
engages with a corresponding steel piece on the exhaust 
lever H, and prevents the exhaust valve G from closing. When 
this valve is held open no partial vacuum can form in the 



chap, vin] OIL AND PETROL ENGINES 



231 



r- X" n 




C 

'5b 

a 



u=. -h O 





Oh 



Q 



1 

o 

bD 
O 
,4 






+3 

o 

«2 



CO 
CO 

6 

M 

ft 



232 THE INTERNAL COMBUSTION ENGINE [chap, vin 

cylinder during the charging stroke of the piston because there 
is free communication with the atmosphere through the ex- 
haust valve, and consequently no charge of oil and air can 
be drawn into the cylinder. The vaporizer for combining air 
and oil into an explosive mixture is shown in section in Fig. 
64 and consists of a cast-iron chamber A securelv bolted to the 




Fig. 64. — Campbell Oil Engine., illustrating operation of vaporizer. 

cylinder and in direct communication with the combustion 
chamber. Into the top of this chamber the inlet valve plug 
B is fitted and this plug contains the seat of the inlet valve 
C [see Fig. 63). The inlet valve C is kept closed by a light spring 
D and only opens during the charging stroke of the piston 
when a partial vacuum is formed in the cylinder. Oil is 
admitted through the annular space or groove F. and passes 
through small holes in the valve seat and into the vaporizer 
when the inlet valve leaves its seat. Air is admitted through 



(hap. viii] OIL AND PETROL ENGINES 



233 



INDICATOR SCREW 



CYLINDER JACKET 



the pipe M and passes through the inside of valve plug B, 
carrying the oil with it. The ignition tube E is screwed into 
a boss on the chamber A. The tube and the whole of the 
vaporizer is kept hot by an external lamp.* During the 
charging stroke of the piston, a partial vacuum is formed in 
the cylinder and the charge of oil and air is drawn through 
the inlet valve and sprayed against the heated sides of the 
chamber A. The mixture then passes into the cylinder, is 
compressed on the return stroke of the piston and then fired 
by the heat from the 
ignition tube. 

146. The Hornsby 
Type of Vaporizer is 
also worth studying. 
This type of vapor- 
izer is shown in Fig. 
66 and to show how 
the vaporizer is fitted 
in place the diagram 
includes the cylinder 
also. When it is de- 
sired to start the en- 
gine a lamp is placed 
under the vaporizer 
chamber until the 
latter is at a sufficient 
temperature to ignite the oil which is pumped into it. This 
lamp is withdrawn once the engine is started, as the heat of 
explosion is sufficient to keep the temperature up to the 
requisite point. The oil tank is under the engine, and from it 
the oil is forced by a small pump into the vaporizer just at 
the moment when the piston is starting on its out-stroke and 
is drawing in the air necessary to combustion. *f The supply 

* In some later engines a large ignition tube is used which is able 
to retain enough heat from each explosion to fire the next, so that the 
lamp may be withdrawn once the engine has been started. 

t In construction this type of engine is similar to the " Hot bulb " 
or " Semi-Diesel " engine. (See par. 147 for comparison with the 
" Diesel.") In these latter engines, however, the fuel is not injected 
into the vaporizer until the piston has reached the end of the com- 
pression stroke. 




Fig. 



65. — Enlarged view of Exhaust valve of 
Engine shown in Figs. 63 and 64. 



234 THE INTERNAL COMBUSTION ENGINE [chap, vni 




of oil is controlled by the governor in the following way. 
The oil passes through a valve-box with two valves, one of 
which leads to the vaporizer and the other leads to an overflow 



Chap, viii] OIL AND PETROL ENGINES 



235 



from which the oil can flow back to the tank. If the speed 

rises beyond the required point the governor opens this latter 

valve and the quantity of oil getting into the vaporizer is 

therefore reduced. On the return stroke of the piston the 

mixture is compressed and some of it forced back into the hot 

vaporizer, where the temperature is so high that ignition 

occurs and a working stroke is therefore made by the piston. 

The vaporizer chamber can, of course, be taken out and 

cleaned when desired. It is found, however, that even when 

working on quite heavy unpurified oils very occasional cleaning 

will suffice. 

Fuel \^lv£. 

£2, 



air Valve: 



Exhaust Valvs 



147. Diesel and 
semi-Diesel Engines. 

— Both these types 
of engine work with 
a heavy oil fuel. In 
both cases air only is 
admitted during the 
suction stroke, and 
in both the com- 
pression is carried to 
a much higher pres- 
sure and tempera- 
ture than is possible 
in oil engines in 
which an explosive 
mixture of air and 
oil vapour are com- 
pressed together. 
The first Diesel en- 
gine was built at 
Augsburg * in 1897, and since then many thousand engines 
have been constructed for the smaller naval ships, for 
power generation and for other purposes. In this engine 
the compression is carried to 500 lb. per sq. inch (correspond- 

* Dr. Rudolph Diesel on "The Diesel Oil Engine," Proc. I. M. E. 
1912. Diesel's original idea had been to follow the constant tempera- 
ture cycle, but ths large siz3 of the engine in proportion to the indi- 
cated power made the mechanical efficiency extremely poor and the 
cost very high ; the plan was therefore abandoned. 




Fig. 67.- 



-Cylinder Head and Valves of Diesel 
Engine. 



236 THE INTERNAL COMBUSTION ENGINE [chap, viii 

ing to a compression ratio of about 12) and in the semi- 
Diesel to about 150 lb. per sq. inch ; whereas in the ordinary 
type of oil engine the compression cannot be taken much 
beyond 60 to 70 lb. per sq. inch (gauge pressure) without the 
charge pre-igniting. The compression space in the Diesel 
engine has to be exceedingly small ; and to facilitate this the 
arrangement at the head of the cylinder is as shown in Fig. 67. 
In the Diesel and semi-Diesel engines pre-ignitions of the 
ordinary kind are equally impossible, as there is no fuel present 
during any part of the compression stroke — although if from 
defective construction the oil inlet-valve of a Diesel engine 
should leak, there is a risk that explosion may take place 



500- 




250- <• 



Fig. 68. — Indicator Diagram from Diesel Engine. 



during the compression stroke and that the engine be damaged 
unless massively built. This danger is eliminated in the 
semi-Diesel engines, which have the oil supply forced into the 
cylinder by the action of a force pump which comes into action 
exactly on the dead point — with this arrangement the only 
result of a leaky valve would be leakage jrom and not into the 
cylinder. 

In the Diesel engine the fuel is sprayed in through the fuel 
valve shown by air at 800 lb. per sq. inch as soon as the valve 
opens. The compression stroke has previously compressed 
the air and exhaust products to 500 lb. per sq. inch, corre- 
sponding to a temperature of about 600° C. The oil vapour 
therefore burns as it enters, and the pressure is maintained 



chap, vin] OIL AND PETROL ENGINES 



237 



at about 500 lb. per sq. inch during an appreciable portion of 
the outward stroke of the piston until at a given point the oil 
supply is cut off and expansion takes place. Fig. 68 shows an 
indicator card typical of this cj^cle. In computing I.H.P. 
from such a card, deduction needs to be made for work done 
in the air-compressor. Every Diesel engine is equipped 
with an air compressor for maintaining a supply of air in the 
starting and air injection vessels. The pressure is usually 
maintained in these vessels at from 800 to 1,000 lb. per sq. 




Fig. 69. — Three-cylinder " Mirrlees Diesel " Oil Engine coupled direct to 
90 K.W. Generator. For Birkdale District Electric Supply Co. 



inch and must not be allowed to fall below about 600 lb. per 
sq. inch, otherwise the compression pressure in the working 
cylinder would prevent the fuel entering and the engine could 
not be started. 

The Diesel engine needs no ignition device. In the semi- 
Diesel engine, however, the compression temperature is not by 
itself high enough to ignite the oil, which is therefore made to 
enter a specially hot chamber at the end of the cylinder. 
Contact with the hot walls of this chamber in the presence 
of the heated air ignites the charge. This hot chamber is 
heated by a lamp on starting, but afterwards maintains itself 



238 THE INTERNAL COMBUSTION ENGINE [chap, viii 



at a sufficient temperature. The whole of the oil is injected 
at once and not gradually, as in the Diesel. 

It is claimed that the fuel consumption of a Diesel engine 
need not be more than 0-45 lb. of oil per B.H.P.-hour at full 
load. If the oil have a calorific power of 15,000,000 ft. -lb. 
per pound, this is equivalent to the engine yielding 1,980,000 
ft.-lb. for every 0-45 X 15,000,000 ft.-lb. put into it, giving 



a-Air Suction Valve 
brExhaust Valve 
c.-Fuel Injecting Valve 
dr Starting Valve 
erStarting Lever 





Fig. 70. — Sectional view of Diesel Oil Engine (Mirrlees, Watson & Co.), 
Note position of inlet valves. See also Fig. 70a. 

a brake-thermal efficiency of -?— - or nearly 30 per cent. 

J 6,750,000 J * 

This is a high efficiency, and the reason why it can be obtained 
is mainly on account of the high compression employed. 
Reference to p. 85 will show that the " gas standard " effi- 
ciency for a similar compression ratio, of about 12, is 52 per cent. 
The Diesel engine may be made two-stroke or four-stroke 
as desired ; in the former case it is easily made reversible, 



chap, viii] OIL AND PETROL ENGINES 



239 



which for marine work is convenient. Any widespread use 
of this engine either on sea or land depends very largely on a 
supply of residual oil fuel or of a suitable tar-oil being obtained 
at a cheap price. 



Top posit/on 

6 

-^c ■'-■ Middle posit io n 




i\f )Siarting Vessel 
Vjy Pressure 






Fig. 70a. — Side view of Engine shown in Fig. 70. 

148. The Thornycroft marine engine can be operated with 
either petrol or paraffin. It is, of course, easier to work a 
marine engine on paraffin than a land one, as in the former 
the starting torque required is very slight, and the speed at 
which the engine runs is much more even. There are, in 
short, no hills to climb. 

The Thornycroft engine is illustrated in Figs. 71 and 72, 
and the following description will help to elucidate them. 

In the first place it will be noticed that the engine is essen- 
tially a marine one, the bearing arms being cast on the bottom 



240 THE INTERNAL COMBUSTION EXGIXE [chap, vm 




half of the bed-plate, and large doors being fitted in the upper 
half to enable adjustments to be made to the bearings 
etc. It will also be noticed that the engine is substanti- 
ally built and suitable for heavy continuous running at 
full power. 

The cylinders M are cast in pairs with large water-jackets X 

surr ounding 
them ; these 
water-jackets 
extend suffici- 
ently far down 
to enable the 
working parts 
of the cylinders 
to be co m- 
pletely covered. 
is the piston 
fitted with five 
piston rings ; 
P the connect- 
ing rod working 
on the gudgeon 
pin Q fitted 
with a solid 
bush. R is the 
crankshaft, and 
it will be 
noticed that 
the cranks are 
at 180 degrees 
with each 
other. The 
main bearings 

are shown at S. and are of considerable length. The 
bottom ends T of the connecting rods are adjustable, and 
it will be noticed that to assist lubrication the cap and 
bottom half brasses are left slightly narrower than the 
top half. The pinion U on the crankshaft drives two fibre 
wheels V connected to the half -speed shafts. The free-wheel 



Fig. 71. — General Arrangement of Thorny croft 6* X 
Marine Petrol or Paraffin Engine — End view. 



chap, viii] OIL AND PETROL ENGINES 



241 



starting arrangement is shown at W, together with the handle 
and chain wheels. The sparking plugs are shown at XX and 
are of the positive make-and-break type worked by] tappets 



.w 



heum 



M M N. 




Fig. 72. — General Arrangement of Thornycroft 6" 8" Marine Petrol or 

Paraffin Engine — Side view. 

YY. Advance sparking gear is worked by the lever Z, and 
half compression for starting by the lever A. The exhaust 
collecting-branch is water-cooled. 



242 THE INTERNAL COMBUSTION ENGINE [chap, viii 

149. The Petrol Engine. — The principle of working of a 
petrol engine is just the same as that of a gas or oil engine — ■ 
so much so that petrol engines have not infrequently been 
coupled up to suction producers and run for a time as gas 
engines. Although this is so it must be borne in mind that 
owing to differences in the nature of the working fluid the 




Fig. 73. — 16 H.P. Two-Cylinder Albion Petrol Engine for Motor Wagons. 

proportions of the engines require to be designed separately 
for each method of working. In a petrol engine the working 
fluid is a mixture of air with about 2 per cent.,, by volume, of 
petrol Vapour. This mixtme is formed by admitting both 
air and petrol to a device called a carburettor. From the 
carburettor the mixture passes to the engine — most often 
through a throttle valve of the butterfly wing variety. The 
proportions of air and petrol are adjusted by having variable 



chap, viii) OIL AND PETROL ENGINES 



243 



inlets for the air and controlling them by hand or by a governor. 
One, two, three, four, six or eight cylinders may be used to 
make up one engine. The 
cheaper cars usually have two 
or four cylinders, whilst six 
cylinders are often fitted to 
the larger ones. The more 
cylinders an engine has the 
more uniform is the turning 
moment and the lower the 
speed at which the engine 
can be run without stopping. 
This is an important point, 
and it is usually discussed 
under the title of " flexi- 
bility."* Maximum H.P. is 
usually obtainable at from 




Fig. 74. — Typical Piston of Petro 
Engine. 



1,500 to 2,000 r.p.m., but it is often desired to run at much 
lower speeds. As the car speed is required to have a very 
considerable range, and as full power should be available at low 




Radiator 



/ 



a 



Front Hoad ./heel 
Front Ax/e 

ngine 



Rear Road Wheel 



Fly Wheel 

and Clutch 



a 



■■oooo— {h 



/ 



Gear Box 



Propeller Shaft 



X) 



a 



lO Rear Ax/e 
Bevel Drive 



X) 



Fig. 75. — Line Diagram of arrangement of Motor Car Chassis. 

with Fig. 76.) 



(Compare 



as well as at high speeds, variable gearing has to be introduced 
between the engine and the road wheels. 

This brings us to the consideration of the mechanism by 
which the power of a petrol engine is transmitted to the road 
wheels of a car. This is shown diagrammatically in Fig. 75, 
whilst in Fig. 76 is seen a Talbot Chassis showing how the 
arrangement is carried out in practice. 



244 THE INTERNAL COMBUSTION ENGINE [chap, viii 



The engine is fitted to the car so that the crankshaft points 
in the direction of motion of the car ; this shaft is continued 







O 

H 

f-t 
© 

.g 

i— i 

o 

i 
X 

■ iH 

w 

O 



03 

Q 



d 

M 



from the front of the car to the back and its continuation is 
called the propeller shaft, owing to its being similarly placed 
to the propeller shaft of a screw steamship and actually being 



chap, viii] OIL AND PETROL ENGINES 



245 



the propeller shaft when used in a marine motor. This shaft 
transmits power by bevel, worm, or chain gearing to the rear 
axle of the car, which of course is at right angles to it. In 
order to be able to alter the velocity-ratio between the engine 
and rear axle a gear box is fitted in the position shown, and 
by means of a lever worked by hand, the velocity-ratio can 
be altered at will. 

The mechanical efficiency of the transmission from engine 
cylinder to road wheels is variously stated as anything from 
60 to 80 per cent. The following table based on tests by 
Riedler shows generally the way in which the losses are incurred. 





H.P. at full speed on level 




Benz 

Car 

(84 m.p.h.) 


Adler 
Car 
(71 m.p.h.) 


Daimler - 

Knight 

Car 

(50 m.p.h.) 


Bussing 
Wagon and 

Trailer 
(16 m.p.h.) 


Loss in transmission . 
Total rolling loss . 
Front wheel friction and 

windage .... 
Air resistance . 


H.P. 
17 

27 

4 

52 


H.P. 
12 

231 

36 


H.P. 
6 
9 

4 
22 


H.P. 
13 
17 

4 
4 


Total H.P. . . 


100 


75 


41 


38 



The effect of speed upon the air resistance is very well 
seen from these figures. It rises from the 4 H.P. of the 16 
m.p.h. vehicle to 52 H.P. for the 84 m.p.h. car. 

150. Sleeve and Rotary Valves for Petrol Engines— A few 
petrol engines are fitted with what are known as ; ' sleeve 
valves " instead of poppet valves. Sleeve valves work on 
much the same principle as a steam engine slide valve. The 
moving sleeve works in between the cylinder liner and the 
cylinder wall, and the liner itself may be made to slide too. In 
this way timed openings and closings of valve passages are 
possible. A further proposal is to use rotary valves, in 
which, by the steady rotation of one long distributor, all the 
cylinders are controlled. At present, however, experience is 
in favour of the poppet type of valve. 



246 THE INTERNAL COMBUSTION ENGINE [chap, vm 

151. Aeroplane Engines. — Aeroplane engines, although 
generally similar in principle to motor-car engines, require to 
be made much lighter. The seven-cylinder Gnome rotary 
engine is compact and very light for the horse-power developed, 
its weight being only about 3 lb. per horse-power. It has been 
much used for aeroplane work, but owing to the difficulty of 
silencing the exhaust from the rotating cylinders, and to its 




Fig. 77. — Wolseley Aeronautical Engine. 

large lubricating oil consumption, it is not so desirable, 

especially for military purposes,* as a non-rotary engine 

which, although perhaps heavier, can have a silencer fitted. 

In Fig. 77 is shown a small, 60 H.P., non-rotary engine 

* At the War Office trials in 1914 the chief prize was awarded to 
the 100 H.P. water-cooled Green engine. Smaller awards were given 
for aircraft engines of the following makes — Dudbridge, Wolseley, 
Beardmore, Gnome, Argyll, British Anzani, Sunbeam. 



chap, viii] OIL AND PETROL ENGINES 



247 



built by the Wolseley Co. for use in aircraft. The engine 
has 8 cylinders, each 3f in. bore X 5 J in. stroke. The 
cylinders are of the separate type, mounted on an aluminium 
crank case, and placed at an angle of 90 degrees laterally. 
The cylinder jackets are of spun aluminium, screwed and 
jointed to the combustion heads ; the induction valves are 
atmospheric. The pistons are of drawn steel, machined and 
ground to gauge. The engine is guaranteed to develop con- 
tinuously not less than 60 B.H.P. at 1,250 r.p.m., with a 
petrol consumption of not more than 0-7 pints per B.H.P. 
hour, and a maximum of 68 B.H.P. at 1,400 r.p.m. for a 
duration of 10 minutes. The total weight of the engine as 
specified, complete with magneto, wiring, plugs, all water 
pipes on engine, water pump, oil pumps, piping and connex- 
ions, but exclusive of flywheel, exhaust pipes and silencer, 
does not exceed 300 lb., or 5 lb. per H.P. obtainable. 

Particulars * are given on p. 248 of the more important 
features of the engines exhibited at the 1914 Aero Show at 
Olympia. 

152. Carburettors. — The function of a carburettor is to 
intermingle the petrol or other fuel with the air, so that an 
explosive mixture is formed which can be admitted forthwith 
to the cylinder. It is possible either to allow only a portion 
of the air to pass through the carburettor and then to add 
additional air to the mixture so as to bring it to the required 
proportional composition, or, on the other hand, the whole 
of the air may be passed through the carburettor. Some 
petrol comes over in the form of a liquid spray, and air carrying 
such a spray is quite easily explosive. 

The " intermingling " is caused in one of two ways : (1) by 
the jet method (which is the most common), or (2) by the 
surface evaporation method. In the former the jet may be of 
either of the varieties shown in Figs. 78 and 79. In the former 
the air sucked through B, on the opening of the valve, causes 
petrol to rush up the pipe A, past the screw- adjusted inlet 
opening to a small hole on the conical seating of the valve. 
The lift of the valve therefore not only admits air but uncovers 
the small petrol hole up which a jet of petrol at once squirts. 
* The Automobile Engineer, April 9, 1914. 



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chap, viii] OIL AND PETROL ENGINES 



249 




Fig. 78.— .4. Petrol inlet to Con- 
troller. B. Inlet pipe to Engine. 
G. Needle valve to regulate flow of 
petrol. 



Then the petrol, having so 
low a vaporizing point, at 
once turns into vapour and 
forms with the air an explosive 
mixture. The screw adjust- 
ment — or needle valve as it is 
called — allows the richness of 
the mixture to be adjusted. 
Fig. 79 shows a better and 
more familiar way of doing the 
same thing. Air is sucked in 
past the nozzle of the jet F and 
out by the opening K. In 
rushing past the jet it sucks up 
a petrol spray, which evapor- 
ates as it mixes with the air. 
On the left of the figure is seen the float chamber for keeping 
the petrol level constant. It operates much as does a ball and 
cock feed to a water cistern. B is a needle valve which gets 
pushed down on to its seating by the levers D when the float 
C rises to the top. This stops more petrol coming in until 
the petrol-level sinks so much as to let the float down till 

the levers open the 
needle valve again, 
when more petrol 
flows in. The 
weight of the float 
is so adjusted that 
the petrol-level is 
kept at just the 
right height. It is 
the custom to have 
the petrol standing 
just below the top 
of the jet, but it 

Fig. 79. — Jet Carburettor and Float Chamber. works even if 
A. Petrol inlet. B. Needle valve. G. Float _ . , , 

which closes the needle valve B through Standing mucn De- 

the levers D when the petrol reaches the level low the top of the 

BE. F. Petrol jet. G. Air nozzle. K. Inlet . . _ . f , 

pipe to engine. jet. Evidence ot 




250 THE INTERNAL COMBUSTION ENGINE [chap, viii 

this is seen in instances in which the float chamber is sucked 
quite dry during the running of the engine when the petrol 
inlet pipe A has got choked up in some way. The principle 
of the working of the jet will be gone into later. An effici- 
ent type of a surface carburettor is shown in Fig. 80, which 
illustrates a carburettor used on a Lanchester engine. The 
principle of its working is obvious from the diagram. The 
air passing over a large petrol-soaked surface takes up petrol 
vapour. 

All the carburettors described work best with a certain 



-AIR, 




Fig. 80. — Lanchester Surface Carburettor. 



velocity of flow of the air. When, however, the engine runs 
very fast or very slow the air velocity changes accordingly 
so that the carburettor sometimes gets more air, and some- 
times less, than it wants. If the flow of air be increased it 
is found that too much petrol is taken up, so it is customary 
to arrange for only part of the air to pass the jet and for the 
rest to be added to the mixture without passing the jet at all. 
It is best to arrange for this adjustment to be made auto- 



chap, viii] OIL AND PETROL ENGINES 



251 



matically, and Figs. 81 and 82 show how this can be done. 
The former shows the Krebs automatic carburettor. When, 
owing to increase of piston speed, the suction on the air increases, 
the leather diaphragm O is sucked down against the weak 
spring P and opens a valve at M so that air can flow in and 




Fig. 81. — Krebs Carburettor, in which the opening to the extra air supply 
is controlled by the suction of the engine. 

mingle with the air which has entered at G and has passed the 
jet F. L is the throttle valve controlling the quantity of the 
mixture which is allowed to pass to the cylinder by the pipe K. 
Fig. 82 shows another way of doing the same thing. As the 
suction increases the extra air comes in through the valve 
M and joins at K the part which has come in over the jet F. 



252 THE INTERNAL COMBUSTION ENGINE [chap, viii 



There are many other ways, easily devised, of applying the 
same principle. 

Owing to the heat absorbed by the evaporation of the 
petrol it is usual to warm the entering air slightly. This 
is done by putting the air inlet pipe nozzle close up to one of 
the exhaust pipes so that the air in rushing past the hot pipe 
gets warmed slightly. Of course the fact that the whole 
of the carburettor is under the warm engine bonnet helps to 

keep the tem- 
perature from 




falling 



too 



V/////aA 1 1 V/////S . of special forms 

of carburettor 



low. 

When paraf- 
fin is used as a 
fuel much more 
heat is neces- 
sary.* 

153. Special 
Forms of Car- 
b urettor . — 
There are a 
great number 



Fig. 82. — Automatic Carburettor working in a generally for which the 
similar way to the Krebs. The opening of the i nYeil torS claim 
valve M depends on the suction. 

remarkable ad- 
vantages. Of these the best known are the White and 
Poppe, the Claudel-Hobson, and the Zenith, but there are 
many others in widespread use. Having regard to the great 
variations in the manner of working of these carburettors, 
it is surprising that so many of them work so uniformly 
well. The White and Poppe is illustrated in Fig. 83. It is 
probably the most successful of them all in respect of fuel 
economy. It has no additional air inlet, and keeps the mix- 
ture correct by manipulating the jet and the air throttle. 
The jet is placed in the axis of a cylindrical chamber across 
which the air flow is directed. This chamber is enclosed in a 

* Vide Par; 141. 



chap, viii] OIL AND PETROL ENGINES 



253 



metal sleeve, and the whole has a circular airway drilled through 
both sides. As the chamber is caused to rotate slightly, the 
air passage is restricted. This restriction is made also to 
affect the jet owing to the petrol passage-way up the jet being 
drilled a little eccentrically to the axis of the jet. A cap 
similarly drilled fits over the jet, and as the jet-cap and the 
chamber rotate through an angle, the effective jet opening is 
decreased in the same proportion as in the throttling of the 
airway. This proportion is ob- 
tained by the fact that in each 
case it is a circle sliding over a 
circle, and that both are fully 
opened and fully closed, to- 
gether. The illustration shows 
a double sleeve, the parts of 
which can be set at a fixed rela- 
tionship to one another as a 
means of adjustment. 

154. Heating Air Supply to 
Carburettor. — The various liquid 
fuels used in internal com- 
bustion engines require different 
methods of carburation.* With 
light spirits like petrol it is 
only necessary to warm the 
air which passes over the jet, 
or to jacket the carburettor 
with the warm water which 
circulates through the radia- 
tor. But with a fuel like 

paraffin it is necessary to heat either the air or else the mixture 
very considerably. The former is sometimes done by passing 
the air through tubes heated to a high temperature by the hot 
exhaust gases circulating around them. This hot air is then 
passed over the paraffin jet, and the paraffin is carried along 
partly as spray and partly as vapour. This mixture is then 
too hot to enter the cylinder, and has to be cooled by mixture 
with some cold air. But even so it has to enter the cylinder 

* See Par= 141. 




Fig. 83. — Interior of White and 
Poppe Carburettor. 



254 THE INTERNAL COMBUSTION ENGINE [chap, viii 

hotter than is customary with petrol, and a less weighty charge 
is therefore employed which leads to something like 10 or 15 
per cent, less horse-power being developed. When paraffin 
is used the compression pressure needs to be lowered to about 
65 lb. per sq. in. instead of the figure of 80 lb. per sq. in., or 
more, which is usual for petrol (both gauge pressures). As was 
stated in par. 135, paraffin is less homogeneous than petrol, 
and there is usually some carbon deposited ; the cylinders 
therefore need more frequent cleaning. The presence of this 
deposit tends to induce pre-ignition, and for that reason the 
compression ratio is kept low. 

155. The Cottrell Paraffin Carburettor. — This carburettor 
is illustrated diagrammatically in Fig. 84. C is the pipe which 
receives the air and paraffin spray coming over from the jet in 
the carburettor marked H. When the fuel gets to the branch 
pipe it divides right and left to either end of the vaporizer 
M. M is shown in section at the lower right-hand side of the 
figure. It consists of a corrugated pipe which is surrounded 
by hot exhaust gases and conveys in its interior the air and 
paraffin mixture. This corrugated pipe has to be kept hot. 
In starting the engine cold, provision is made for working on 
petrol for two or three minutes and then, the pipes M having 
got hot, the paraffin is turned on. At B there passes a mixture 
of heated air and paraffin vapour. The air is much less in 
proportion than would ignite, so at F an adjustable inlet is 
fixed to admit more air until the mixture is of the correct 
proportions. The purpose in not letting all this air in earlier 
is that with a less proportion of air the paraffin particles get 
more effectively heated and the velocity of passage through 
the vaporizing tube is slower. 

A variation of this arrangement has been tried for use in 
the tropics, whereby air only was passed through the star 
tubes M, then through a lagged pipe to an ordinary jet cham- 
ber. This alternative arrangement has worked well, but in 
temperate climates hardly seems so effective as the unmodified 
type of carburettor. To begin with, the paraffin draws all 
its heat from the air which sweeps it along, instead of by 
actual rushing contact with the hot vaporizer tubes. Further, 
the mixture enters the cylinder much sooner after its creation 



chap, viii] OIL AND PETROL ENGINES 



255 



t han in the other arrangement, and it is evidently advantageous 
to allow time for the paraffin vapour and air to mix intimately 
with each other. A drop in horse-power in the engine must 
be expected of 10 to 15 per cent, compared with the horse- 
power obtainable when using petrol. This loss is chiefly due 




Fig. 84. — Cottrell Paraffin Carburettor. Shown diagrammatically. 



to the higher temperature of the entering charge which for 
a given cylinder volume naturally reduces the weight admitted. 
There is also a loss owing to the necessary lowering of the com- 
pression ratio and consequent lowering of thermal efficiency. 
It has sometimes been thought that this lowering of the 
compression is due to fear of the charge being pre-ignited 



256 THE INTERNAL COMBUSTION ENGINE [chap, vni 




through the low tem- 
perature at which 
paraffin vapour and 
air ignite spontane- 
ously ; but the real 
reason is that given 
in the previous para- 
graph. 

There is a gain, 
however, in that the 
calorific value of paraf- 
fin per pound is 
about 18,000,000 ft.- 
lb. against about 
15,000,000 for petrol; 
also an advantage is 
found in the smaller 
consumption of lubri- 
cating oil owing to the 
lubricating properties 
of the paraffin itself. 

156. The Thorny- 
croft type of paraffin 
carburettor is illus- 
trated in Fig. 85. Its 
manner of working is 
generally similar to 
that of the Cottrell, 
but the heating sur- 
face is less in pro- 
portion. It works well 
in practice, and its 
mode of operation is 
as follows : — 

The oil is drawn 
into the vaporizer to- 
gether with a certain 
amount of air by the suction of the engine ; this mixture is 
then passed through a tube which is kept heated to a fairly 




Fig. 85. — Thornvcroft Paraffin Carburettor. 



chap, viii] OIL AND PETROL ENGINES 257 

high temperature by the exhaust gases coming from the engine. 
This thoroughly vaporizes and intimately mixes the vaporized 
oil and air. The mixture is then passed through a spiral 
separator, which separates any solid matter from the vapour, 
is mixed with extra air as required to form an explosive mix- 
ture, and then passed through the throttle to the cylinders. 
In the drawing, A is the inlet valve for both oil and air, the 
valve being under the action of spring B, which normally keeps 
the valve closed and the oil supply C shut off ; the oil enters 
by holes in the seating. The mixture then passes along the 
annular space EE which is kept heated to a high temperature 
by the exhaust flowing through the centre of this annular 
chamber as shown at F. The annular chamber, it will be 
noticed, is fitted with gills G to enable a maximum amount of 
heat to be supplied to the mixture. H illustrates the separator 
for removing the solid particles from the mixture, and J the 
" extra-air " inlet, under the control of the spring K. The 
tension of this spring and also of that governing the inlet of 
the mixture to the vaporizer can be varied by a screw and nut 
as shown. This adjustment is made when the engine is on the 
test-bed before the brake trials. The outlet from the vaporizer 
to the motor is by pipe L. There are numbers of other paraffin 
carburettors, but the principle of operation is generally similar 
to those above described. 

157. Theory of Jet Carburettors. — The energy equation for 
the flow of any fluid (liquid or gas) is as follows — see Perry's 
Applied Mechanics : — 



J- I — +h= constant (1) 

In J on 



2g J w 
This is true for any stream line. 

v = velocity of fluid in ft. per sec. 
g = 32-2. 

p = pressure in lb. per sq. ft. 
w = weight in lb. of one cu. ft. 
h = height in feet above datum. 

If this equation be applied to the flow of air through the 
carburettor due to the suck of the engine, it may be simplified 



258 THE INTERNAL COMBUSTION ENGINE [chap, viii 

in inany ways. We want to find the amount by which the 
pressure in the rushing air is made lower than the atmospheric 
pressure owing to the suck of the engine pistons. We start 
with air at atmospheric pressure p , and density w OJ at no 
velocity, and we end with air at velocity r , pressure p, and 
density w. It can then be shown from equation (1) and the 
adiabatic relation for air that : — 

C \Po —P ) • • ( 2 ) 



2g y— 1 

It is, however, possible to use a simpler expression than this. 
Equation (2) assumes that there is no heat lost or gained as 
the air passes through the carburettor, which is not strictly 
true. Since some degree of approximation is necessary for sim- 
plicity we may without any more serious inaccuracy neglect 
the change in density of the air, and it then follows from 
equation (1) that : — 

dp= W °' V ° 2 (3) 

The pressure at the top of the petrol jet is therefore lower 
than the pressure on the surface of petrol in the float chamber 
by dp where dp is given by equation (3). A similar argu- 
ment* to the above will show that the flow of the petrol is deter- 
mined by a formula of the same type. For a liquid such as 
petrol in which w is independent of p. equation (1) becomes 

V 1) 

1- — +7z= constant. 

2g T w 

Applying this equation to the stream line which begins at 
the free petrol surface in the float chamber and ends in the jet 
spray, and assuming that the top of the metal jet is a height h 
above the petrol level (so that petrol has to rise through a 
height It in the jet before it gets to the actual nozzle) we have 

o+^-+o=— +o + h 
w 2g 

where u = velocity of flow of petrol and w = density of petrol 

(i.e. the weight per cubic ft.). 

* Neglecting viscosity. 






chap, viii] OIL AND PETROL ENGINES 250 

v 2 Sp 

2g~~ w 



Therefore — = l ~ — h 



Now by equation (3) : — dp—— ° 

so that t = lV ^-h 

2g 2wg 

on 

or v 2 = —°v 2 —2gh (4) 

w 

This shows that v , the velocity of air flow, must have the 

/ w 
value V 2gh~ before any petrol will flow at all. It is a mat- 
w 

ter of common experience that if the rate of air flow doubles 
the petrol flow more than doubles. Let us see if this is so 
according to this formula. 

First, let v = a, and then equal 2a. The ratio of the 
square j of the petrol flow in the two cases should there- 
fore, according to experience, be more than 4. By formula 
(4) it is 

w 



w 



Act, 2 — 2gh 



^a 2 -2gh 

to 



Ggh 



w °« 2 —2gh 
w 



(5) 



It will be interesting to get some quantitative figures for 
this. What, for instance, will be the ratio ii h = 0-04 feet (or 
\ inch) and a is 5,000 ft. per minute (83*3 ft. per sec.) ? 

Petrol has a density of about 0-72 so that 1 cu. ft. will weigh 
0-72 X 62-3 = 45 lb. Whereas 1 cu. ft. of air weighs 0'075 
lb. at atmospheric temperature and pressure. 

According, therefore, to equation (5) the square of the ratio 
of the two petrol velocities will be 



260 THE INTERNAL COMBUSTION EXGIXE [chap, viii 

6X32-2X0-04 



:* + 



^L'V- (64-4x0-04) 
45 

7-72 



^-257 

600 

The critical velocity is clearly 

= V 2gh— = V 2X32-2X004X600= \/l550=39-3 ft 

w e 

2.360 ft. per min. Until, therefore, the air had this velocity 

i00 
"60 

11-6—2-57 9-0 

= 4-86. 



no petrol would be carried along. If a= the equation 



(5) becomes 



So that when air velocity increases from 5,000 to 10,000 ft. per 
min. the petrol velocity is 2-2 times as much and the mixture 
therefore 1-1 times as rich or 10 per cent, richer. This means 
that the amount of petrol present per cubic foot of air increases 
by one-tenth part. This inequality is most marked when 
the velocity of the air is only a little more than what is necessary 
to feed the petrol, thus if the air velocity be increased from 
2,500 ft. /min. to 5,000 ft. /min. the petrol sucked along would 
be increased by no less than 430 per cent., i.e. the quantity of 
petrol would be 5-3 times as great, giving a richness of mixture 
2-6 times or more than double what it was before. In this 
case, therefore, about twice the quantity of air would be 
needed, i.e. as much again must pass the additional air inlet as 
already passes the jet. This simple theory accounts for part 
of the extra air needed. It does not, however, take account 
of the effect of eddies, that may circulate around the jet at 
high air velocities, ncr does it take viscosity into account. 

It is possible that there are still further reasons why extra 
air is needed when the engine speed increases, but the above 
are certainly some of them. The air velocity is highest when 
the engine is running fast and the throttle wide open. When 



chap, viii] OIL AND PETROL ENGINES 261 

the engine is running fast but is much throttled, as in a car 
running very fast down a slope, the vacuum behind the piston 
never gets filled up with air and the velocity of air past the 
jet is not therefore very great ; going up hill, however, on 
low gear the engine speed is high and the throttle wide open. 
So that the velocity of air past the jet is not solely dependent 
on the engine speed. This makes control of the additional air 
inlet by the centrifugally operated governor not as uniformly 
good as could be wished — it only approximates to extreme 
cases, fitting accurately the average only. When, however, as 
in the Krebs carburettor, for instance, the opening of the extra 
air inlet is controlled by the suction, a much more constant 
mixture is obtained. A carburettor is usually set so that the 
right mixture comes away from the jet at low speeds with the 
extra air inlet closed. Then as the speed rises additional air 
is allowed to pass in. From the preceding calculations it will 
be clear that one cause of the lack of proportionality between 
the air and petrol velocities is the fact that the petrol cannot 
be allowed to stand at a level equal to the height of the jet, as 
if this condition were arrived at too closely there would be a 
risk of the petrol overflowing when standing on grades. A 
further reason which makes it necessary not to run the adjust- 
ment too finely is that the level of petrol in the float chamber 
is bound to vary somewhat not only with the inclination of 
the float chamber but also with temperature and quality of 
supply. In order to keep on the safe side the petrol level 
must be several millimetres below the top of the jet. 

158. Ignition. — The oldest form of ignition was to ignite the 
explosive mixture by a naked flame, which was put into com- 
munication with the cylinder through the medium of a sort of 
slide valve. It is quite obsolete now, but those interested in 
the history of the subject will find a full account in Dugald 
Clerk's book. 

A later and more successful form was Tube ignition, which 
consisted in having a short vertical tube, in communication 
with the cylinder end, heated externally by some means. 
After the engine had been running a short while the lamp could 
be removed (or the gas jet turned out) and the heat of explosion 
was enough to keep the temperature up to the requisite point. 



262 THE INTERNAL COMBUSTION ENGINE [chap, viii 

It is illustrated in Eig. 86. The explosive charge was com- 
pressed by the inward movement of the piston, and a part of 
it passed into the ignition tube, the temperature of which 
raised the temperature of the gas to the ignition point. This 
type of ignition was very largely used for gas engines, but it 
is now universally displaced by some form of electric ignition. 
It was also the first method employed on motor cars, for 
which use it was found to be unsuitable. It is still in use 
with some oil engines. 

Another method of ignition often used with oil engines is to 
feed the fuel into a hot combustion chamber connected to the 
cylinder. This method has already been described in par. 
146. It works well, and even residual oils can be vaporized 
and ignited in this way. The method employed on the Diesel 
engine is of this type. 

159. The chief method of ignition is the electric, and it bids 



./.Shield 




Ignition tube (day) 



\ Asbestos Millboard Liner 



is Burner 



To Cy/i 



lindei 



Timing Valve / L, ; : - . 



Fig. 86. — Ignition Tube and Timing Valve. 



fair to supersede all the others. It is almost equally suitable 
for gas. oil or petrol engines. 

Electric ignition can be carried out by either (1) high- 
tension currents or (2) low-tension currents. 

The high-tension currents may be obtained in one of three 
ways : either (1) by batteries or cells furnishing current to an 
induction coil, or (2) by a small magneto-electric machine 
(called " magneto :: for short) furnishing currents to an indue- 



chap. Mil] Oil, AND PETROL ENGINES 263 

tion coil, or (3) by a magneto furnishing high-tension currents 
direct to the sparking plug. The low-tension currents are pro- 
duced from a low-tension magneto. There are therefore many 
varieties of electric ignition and they may conveniently be set 
out thus — 

Electric Ignition 

l 

i . i 

High tension Low tension 

i i 

i i . . i . i 

Batteries or cells Magneto with High-tension Low-tension 

with induction induction coil magneto magneto 



coil 



(3) (4) (5) 



Coils fitted with Coils fitted with 

tremblers fixed " make-and-break " 

(1) (2) 

The oldest is (1) and it is still seen fitted to some petrol 
engines, although (2) is more common ; (3) is relatively rare 
but was seen in the early Eisemann system ; (5) is common 
practice for engines whose speed is below 300r.p.m. Method 
(4) is growing in popularity, and it has the advantage of 
being simpler to apply to the engine than (5). 

Before describing methods (1), (2) or (3) it will be necessary 
to say something about the induction coil. To those versed 
in electrical matters it is enough to describe it as a transformer 
having a straight iron core and a high ratio of transformation. 

160. Induction Coil.- — The induction coil consists of a soft 
iron core generally consisting of a bundle of straight iron wires, 
and on it is wrapped a layer or two of thick insulated copper 
conducting wire of the primary — or low-tension — circuit. 
Over this are wound many thousand turns of fine insulated 
copper wire constituting the secondary — or high-tension — 
circuit. About 4 volts are applied to the primary circuit and 
the current repeatedly broken and remade by means of the 
magnetism of the iron core attracting a small piece of iron 
mounted on a spring which carries the current. As the spring 
is attracted inwards it loses contact with a platinum point 
and so breaks the current. (To make the break the more 



264 THE INTERNAL COMBUSTION ENGINE [chap, viii 

sudden it is usual to put a condenser in parallel in the circuit,) 
This sudden rise and fall of current in the primary causes 
oscillatory currents in the secondary of a voltage which is 
higher than that in the primary in the ratio of the number of 
coils of wire in one to the number in the other. Owing to the 
effect of the magnetism in the iron core the current in the 
primary does not rise suddenly to its full value. It follows 
in fact the law 

R V 
where 

I = current in amperes. 
V = voltage in volts. 
R = resistance in ohms. 
L = self-induction in henries. 
t = time in seconds, 
e = base of Xaperian logarithms or 2-7183. 

The unit of self-induction is the henry. If S be the rate at 
which the current changes in amperes per second, the back 
electromotive force produced = LxS. One henry is also 
defined to be the self-induction of a coil in which, if the current 
increase at the rate of one ampere per second, the back E.M.F. 
produced is exactly one volt. 

As an illustration of the effect of the above law of rise of the 
current, take the case of a coil in which R = 500 ; L = 5-5 
and V = 50,000. Then the final and steady value of the 

current is clearlv — or 100 amperes. This current grows 

J 500 ^ 

up from zero and it is of interest to calculate how long it will 
take 90 amperes to be the current flowing. 

_ t 
90=1 00(1 — e o-on 



or e o™i=l_ 0-9=0-10 

so that t— about ^ second. 

The current therefore rises by no means instantaneously 
and this leads to the " make " of the primary current, pro- 



chap, vin] OIL AND PETROL ENGINES 



265 



during a much less vigorous spark in the secondary than does 
the " break." The break is almost instantaneous ; the only 
thing that tends to prevent it being so, is the energy of rush 
of the primary current which jumps over the gap in its earlier 
stages. The energy stored up in the flowing current is equal 
to JLI 2 , and it is to provide a convenient swamp to absorb 
this suddenly released energy that the condenser is provided. 

161. High-Ten- 
sion Coil Ignition. 
— The induction 
coil is supplied 
with a low-ten- 
sion current ob- 
tained from either 
batteries, accumu- 
lator cells or a 
suitable magneto. 
In any case the 
principle of work- 
ing is the same. 
The spark gap (see 
Fig. 90) is placed 
in the cylinder as 
shown in Figs. 87, 
88, 89, and 91. A 
rotating contact 
kept at a speed 
proporti o n al to 
that of the engine 
and called a dis- 
tributor d i s t r i- 
butes the current 
to each cylinder just as it is needed. What happens therefore 
is this. The trembling blade on the coil — called the trembler 
— vibrates very rapidly and produces a shower of sparks in 
the secondary (one spark corresponding to each break of cur- 
rent in the primary). During each contact about a dozen 
sparks or more may pass. One good spark would be enough 
and therefore a modification of this method is sometimes em- 




FlG 



87. — Diagram showing mode of working of 
high-tension ignition with coil and accumu- 
lator. A, Accumulator. B, Induction coil. 
C, Contact breaker. D, Trembler. E, Com- 
mutator on end of cam shaft, for closing 
circuit at right moment by bringing metal seg- 
ment F against the brush O. H, Condenser, 
to make break of current sudden. I, Igni- 
tion plug in cylinder. The other end of the 
secondary winding is earthed. 



266 THE INTERNAL COMBUSTION ENGINE [chap, viii 

ployed. Instead of a trembler actuated by the magnetism of 
the iron core of the coil, the current in the primary circuit is 




Fig. 88. — Coil and accumulator Ignition, for a four-cylinder engine, with 
separate coils for each cylinder. A, Accumulator. B, Coils each with 
its own condenser and contact maker. E, Commutator for distributing 
current to the various cylinders at the right moment. /, sparking plugs. 

made and broken by the action of the engine. A mechanical 
make-and-break is fitted to the half-speed shaft of the engine 



\fl W W S(H 




Fig. 89. — The arrangement shown in Fig. 97, except that one trembler 
serves all the coils. This saves having to adjust each trembler until 
all are working at same frequency. G is the common contact maker, 
and N are switches for cutting out coils when necessary. 



so as to produce one spark only in the cylinder. It is possible 
to ring the changes on this form of ignition so as to produce a 
great many varieties, although the differences between them 



chap, vm] OIL AND PETROL ENGINES 



267 



are hardly fundamental. Illus- 
trations, reproduced from Mr. 
Strickland's useful book, are 
shown of several such methods 
(566 87, 88, 89, and 91), and the 
letterpress at the foot of each 
will suffice to show their differ- 
ences. 

162. The Lodge (Sir Oliver 
Lodge) system of ignition is just 
the ordinary coil and accumulator 
ignition in which the high-tension 
current instead of being passed 
direct to the sparking plugs is 
made to charge up the inner 
coatings of two Leyden jars. 
When the jars are " full '' an 
external spark gap placed in 
parallel with the jars breaks 
down and a spark passes. This 




Fig. 90.— High Tension Spark- 
ing Plug. A, MetaL Rod ; 
B, Porcelain Insulating 
Sleeve ; C, Gland ; D, Body 
of Plug screwing into cylin- 
der; E, Sparking Points ; 
F, Electric Wires from 
H.T. Magneto or Coil. 



sudden release of the electric 

charges on the inner coats of the Leyden jar causes such a 
rush of current from the outer coating of one Leyden jar to 

the other, and such a 
violent oscillation to and 
fro of the current after- 
wards that nothing will 
stand in its path. It 
breaks through oil films, 
soot, deposit of all kinds, 
water or anything else 
that there may be on 
the ignition points ; ow- 
ing to its high frequency 
it also tends to take 
straight direct courses, 
and there is little dis- 
position on its part to 
seek any short circuit 




Fig. 91. — The arrangement of Figs. 88 
and 89, except that the secondary 
current is distributed directly, so 
enabling only one coil to be used for 
all four cylinders. The disadvan- 
tage is that the insulation is more 
difficult to ensure. 



268 THE INTERNAL COMBUSTION ENGINE [chap, vm 



-c •- 



U 



- f . Z i - 
. z - Z 



_ i i a ■ 



of a tortuous kind which niay happen to be in exist- 

Kg - shows iiagranunaticallv the arrangements of the 

high-tension circuit. Z'^- 
low-tension circuit is of the 
customary form, except that 
the trembler shown in Fig. 
93 is of an extra sensitive 
form. The distributor is 
placed in the high-tension 
circuit. The makers of this 
iiiiirlir. ?ts^— :-Liin :La: 
owing to the adjustments 
made no possible error in 
the time of firing can arise 
which exceeds 3 * th part 
of a second. Also that in 
virtue of the nature of the 
spark the system is par- 
ticularly suitable for use 
when the fuel used is one of 
the heavier brands of petrol, 
or paraffin or other heavy 
oil which may cause carbcn- 

aceous deposit on the ignition plugs. 

163. Magneto ignition may be either high tension, or low 

tension. No coil is used and no batteries or cells are wanted. 

Iir low-tension 

nr:h: i ::: ::::'• :n :Lr 

principle that when a 

:\u:t::: :- ~\"-~z^ :: 



7::- _"1 — 7 



:^-~" 



: -: . i : - f - 



-Q 



I ■ 



equal to I 

: :; - : : k± 



Ji»e£), and that if L. 



- . .- : -:- 1 . : - 

93. — Lodge Sensitive Trembler. 



the seK-induction. is 
made very great and I. the current, as great as con- 
venient, the energy stored up is so considerable that a 
large or " fat " uk is caused to occur when the 



chap, viii] OIL AND PETROL ENGINES 



269 



y-= 



circuit is suddenly broken. A low-tension magneto, or 
electric generator, is designed so as to cause such a current to 
be passing at the moment when ignition is desired to occur 
and, at the same instant, the circuit is mechanically broken 
in the cylinder and a spark passes. Fig. 94 shows diagram- 
matically the wiring for this system and the sparking plug 
used. A larger view of such a plug is seen in Fig. 95. A 
disadvantage of this system is the introduction of moving 

tappets into the cylinder, and the 
necessary provision of means for 
operating them from outside. 

164. The High-Tension Magneto. — 
In this machine the current is generated 
by a shuttle armature which rotates 
between the poles of strong steel mag- 
nets. The rotation of this armature 
in the strong magnetic field results in 
the induction in its winding of an 
electrical current which is utilized 
for the purpose of ignition. The 
armature is wound in two parts, of 
which one is a primary winding, 
consisting of a few turns of heavy 
wire, and the other a secondary wind- 



Fig. 94. — Low - Tension 
Magneto Ignition. X 
and Y, magneto 
machine shown dia- 
grammatically. A, 
Spark plug. C, Contact 
point where circuit is 
closed and broken. B, 
Lever worked by rod 
running on cam E. E, 
Cam on half-time shaft. 
At the moment when 
the magneto is passing 
its maximum current 
around the circuit, the 
cam causes the circuit 
to be broken at C, so 
producing a spark at 
that point. 





Fig. 95. — Typical Xow-Tension Magneto 
Spark Plug. It will be noticed that this 
system [of ,ignition requires moving con- 
tacts in the cylinder, which the high- 
tension system does not. 



•2 70 THE IXTERXAL COMBUSTION ENGINE [chap, vtii 



ing, consisting of many turns of fine wire. The effect is 
that a high-tension current is given off by the armature. 

as the design practically 
amounts to the inclusion in 
the armature of the windings 
of an induction coil. An 
outside view of this magneto 
is shown in Fig. 96, and its 
manner of working is shown 
in Fig. 97. 

This system has the advan- 
tage that no moving parts 
need to be introduced into 
the cylinder in order to pro- 
duce a spark. The voltage 
is so high that a : " safety 
valve " spark-gap is usually 
fitted in parallel near the 
magneto in order to allow 
anv unduly high voltage cur- 
rent which may be produced to pass across it. The spark 
in this gap is. of course,, of no use except to act as a safety 
valve or bye-pass. 




*r222»>2SW5^ 



Fig. 96. — Outside view of BoschlLT. 
Magneto. (A low-tension mag- 
neto is of generally similar 
shape.) 



S I 

etc ^Z 

~l^# S ' 23 Primary winding 

2 3 4 

Sparking plugs 




Contact 
breaker disc 



Fiq. 97.— High-Tension Magneto Ignition, as arranged for 4-cylinder Engine. 



chap. viii| OIL AND PETROL ENGINES 2 71 

165. Dual Ignition. — In a later form of high-tension magneto 
ignition, an accumulator and coil is added. The coil does its 
own making-and-breaking, but the distributor and the sparking 
plugs are common to both systems. In normal running the 
magneto is switched on ; but when starting the coil is used. 
It is easy to tell which is in use, as the coil makes a buzzing 
noise. This system has become popular since the accuracy 
of manufacture of petrol engines has risen to such a high pitch. 
The fit of the piston, piston rings and valves is now so good 
that any compressed gas there may be in the engine on stop- 
ping will stay compressed for some hours and in most cases 
the engine will start from rest by merely switching on the 
coil ignition, so saving the labour of turning the engine 
round by the starting handle. This system, of course, is 
specially adapted for the petrol engines used on motor 
cars. 

For gas engines, large or small, the ordinary high-tension or 
low-tension magneto is employed. Sometimes the ignition 
occurs at one fixed point in the stroke and sometimes it can 
be varied by hand or by the action of a governor. Some 
engines have two high-tension plugs in series so as to ignite 
the gas from more than one point and so produce a more rapid 
explosion. The ignition plug should never be put at the end 
of a recess or else a pressure wave may be produced which 
will cause detonation and possibly break the cylinder bolts 
and so lead to a bad accident. 

166. Timing of Ignition. — One of the most careful adjust- 
ments of the ignition is its timing. That is to say, the regu- 
lation of the moment of sparking in the cylinder. If the spark 
is late the piston will have moved part of its outward journey, 
with the consequence that the effective working stroke is 
lessened and the mean pressure is lower than it need be. If 
the spark is too early, so that the gases are still being com- 
pressed when the spark comes, there is a knock in the 
cylinder when the explosion occurs. Normally the spark 
should occur just as the piston is at the top of its stroke, 
although since ignition takes a fraction of a second to spread 
throughout the mass of the gas it is necessary when the engine 
is running fast to time the spark to occur a little before the 



272 THE INTERNAL COMBUSTION ENGINE [chap, vni 

dead centre >o that maximum pressure is reached when the 
piston is just beginning its stroke. Engine speed is. how- 
ever,, not the only consideration affecting the timing ; when 
running with weak mixture- the ignition takes longer than 
with rich mixtures so that to use a weak mixture it is necessary 
to "* advance " the spark, i.e. make it occur earlier. It follow-, 
therefore, that in the ordinary ninning of a car the ignition 
requires as much attention as the throttle, if the engine is 
to work at highest efficiency. An additional complication 
arises when coils having tremblers are used with batteries 
or cells., as the -peed of "' trembling " : being naturally in- 
dependent of the speed of the engine, it follows that at high 
engine speeds the sparking in the cylinder is apt to be 
somewhat erratic, sometimes coming early and sometimes 
late. 

In a paper read by W. Watson before the Royal Automobile 
Club an interesting account was given of certain experiments 
undertaken to ascertain the character of the spark in relation 
to power. The engine used was a two-cylinder one.. 3-5 in. 
X 4 in., with mechanically operated valves. The sparking 
plug was screwed into the cap used to close the hole over 
the inlet valve., the spark points being well inside a recess in 
this cap. The whole of the experiments were made on one 
cylinder only, the other being operated with a trembler coil 
and battery. The speed was 950/1,000 revolutions per 
minute. It has often been claimed that a " fat "' spark 
improves the running, and that this was due either to quicker 
ignition of the charge or to more regular firing. Experiments 
with a trembler coil showed that although the weakening of the 
current was found to reduce the mean pressure, yet this could 
be brought hack to its original value by advancing the spark. 
The result of this series of experiments was to lead Watson 
to the following conclusions — 

1 . As far as a petrol engine of the type used is concerned, the 
character of the spark which ignites the charge has no appre- 
ciable influence on the power developed. 

2. With a trembler coil the time at which the spark occurs is 
liable to vary greatly, and on this account the power developed 
may be considerably reduced. 



chap, vni] OIL AND PETROL ENGINES 273 

3. The variation in the time of firing obtained with trembler 
coils is different for different coils, and hence a multi-cylinder 
engine in which a separate coil is used for each cylinder is 
unlikely to develop its maximum power, particularly at high 
speeds ; the reason being that although the tremblers of the 
coils may possibly be adjusted, for some particular voltage, so 
that each cylinder fires at the same point of the stroke, yet 
this adjustment will no longer be true if the voltage of the 
battery alters, particularly if it falls much below the value 
for which the tremblers were adjusted. 

4. When a single coil is used in combination with a high- 
tension distributor, it is of very great importance that the 
current in the primary should never be allowed to fall to a 
value near the critical value for the particular coil. In this 
connexion it may be mentioned that, in Watson's experi- 
ence, when the trembler is so adjusted for any given voltage 
of the battery, i.e. for a given current, that the note produced 
is very clear and " pure," then a very slight decrease in current, 
due to a small fall in the voltage of the battery, will cause the 
timing to be defective, owing to the region of the critical 
current being approached. Hence, with the normal current 
passing — i.e. with the battery fully charged — it is advisable 
to adjust the trembler so as to give a somewhat harsh and 
shrill sound, for then the current may be considerably reduced 
before the critical value is reached. 

5. When selecting a coil, regularity in the working of the 
trembler for considerable variation in the current passing 
in the primary is of more importance than length or fatness 
of spark. Further, a coil taking a small current is to be 
preferred to one taking a large current, since trouble with 
the adjustment of the trembler blade will be decreased, owing 
to the reduced sparking at the platinum points with a small 
current. 

6. Except for the fact that the engine cannot be started on 
the switch, the plain coil with a rapid break on the two-to-one 
shaft seems preferable to a trembler coil, since over a very 
large range of current — in fact, whenever the current is large 
enough to cause the passage of a spark in the cylinder — the 
timing is exactly the same. The advantage of the trembler 

T 



274 THE INTERNAL COMBUSTION ENGINE [chap, yui 



£00 



might be retained by using a switch, so that after the engine 
is started the trembler can be cut out. allowing the coil to 
act as a plain coil, a second condenser being provided. 

The two dia- 
grams shown in 
Fig. 98, obtained 
by Watson, illus- 
trate the advan- 
tage, so far as 
economy is con- 
cerned, of advanc- 
ing the spark more 
than usual when 
employing a very 
weak mixture — 
that is, when driv- 
ing with the extra 
air valve as far 
open as possible. 
The lower figure is 
that obtained when 
the spark is as 
much advanced as is advisable when usinc a full mixture, 
and the I. H. P. at 1,000 revolutions was 2-36. In the upper 
figure the spark has been considerably further advanced, so 
as to allow for the slow burning of a weak mixture, and 
as a result the I.H.P. at 1,000 is 2-76. an increase of nearly 
17 per cent, in power, the consumption of petrol remaining 
the same. 




Fig. 98.- 



-Indicator Cards obtained by 
Watson. 



EXAMPLES 



1. An oil engine uses 0-8 lb. of kerosene per actual H.P.-hour ; one 
pound of kerosene gives out 12,000 C.H.T7. in combustion. What 
is the efficiency of the engine ? B. of E., 1911.) 

2. In the test of an oil engine the analysis of the exhaust gases by 
volume gave : C0 2 = 6-8 per cent. ; 0=11-1 per cent. ; N = 82-1 
per cent. The oil analysis was H = 15 per cent. ; C = 85 per cent. 
Find the excess air and the total mass of products per lb. of oil. 



chap, viii] OIL AND PETROL ENGINES 275 

3. What weight of () is required for bhe complete combustion of 4G 
grams of alcohol (C 2 H 6 0) ? What weight of C0 2 will be formed, and 
what weight of water ? 

4. The following data are taken from the test of an oil engine : — 

I.H.P. = 65. 

Oil used per hour = 45 lb. 

Calorific value of oil = 19,500 B.Th.U.'s per lb. 

lb. of air per lb. of oil = 70. 

Jacket cooling water in lb. per min. = 68. 

Temperature of cooling water, inlet = 62° F. 

Temperature of cooling water, outlet = 138° F. 

Temperature of exhaust gases = 430° F. 

Temperature of engine room = 70° F. 

Specific heat of exhaust gases = 0-24. 

Draw up a table showing, as percentages, how the total heat of com- 
bustion is distributed. 

5. In one pound of petrol there is 0-846 lb. of carbon and 0-154 lb. of 
hydrogen. What is the calorific value of petrol per lb. given that the 
calorific value of carbon is 8,130 C.H.TJ. per lb. and of H 29,100 C.H.TJ. 
per lb ? What weight of O is required for complete combustion of 1 lb. 
of petrol ? (B. of E., 1910.) 

6. The area of a petrol engine diagram is (using the planimeter which 
subtracts and adds properly) 4-12 sq. inches, and its length (parallel 
to the atmospheric line) is 3-85 in. ; what is the average breadth of the 
figure ? If 1 in. pressure represents 70 lb. per sq. inch, what is the 
mean effective pressure ? The piston is 3-5 in. in diameter with a 
stroke of 4 in. What is the work done in one cycle ? If there are 800 
cycles per minute, what is the horse-power ? 

7. A petrol engine working on the Otto cycle has a cylinder 4 in. 
diameter and length of stroke is 4 in. The compression space* is A- 
volume. Assuming the brake thermal efficiency to be 20 per cent., 
find the maximum power which the engine could give, running at 1,000 
r.p.m. if at the end of each suction stroke the whole cylinder were filled 
with an explosive mixture of petrol vapour and air, having a mean 
calorific value of 57 C.H.TJ. per cu. ft. 

8. A 4-cylinder petrol motor develops 60 B.H.P. at 1,500 r.p.m. 
What is the mean turning effect exerted on the crank shaft ? and what 
must be the ratio of the gearing between the engine and the driving 
axle, so that the car speed is 40 m.p.h. ? Assuming that the internal 
resistance of the car machinery is 20 per cent, of the power developed, 
what is the total external resistance against which the car is driven ? 
Diameter of the rear road wheels is 32 ins. 

(B. of E., 1913.) 

9. In a Diesel engine the compression ratio is 15-3 and the expan- 
sion ratio 7-5. The indicator cards give a nett I.H.P. of 201 and the 



_' THE INTERNAL COMBUSTION ENGINE Vhap. vth 

oil consumption was 67 lb. per hour, of calorific value 19,300 B.TL.U. 
per lb. Calculate the ratio of the actual thermal efficiency to the 
thermal efficiency of an ideal engine, receiving heat at constant pres- 
sure and rejecting it at constant volume, the compression and ex- 
pansion being adiahatic and y = 1-4.* 

10. In a motor cycle of 3 I.H.P. the mass of petrol used during a 
4 hours" run at full speed is 8 lb. The highest temperature in the 
engine cylinder is i F. and air is drawn in at 60 c F. Find the 
t hernial efficiency and compare it with that theoretically possible. 
The calorific value of petrol is 18,600 B.Th.U. per lb. 

11. The Gnome petrol engine develops 50 B.H.P. at 1,200 r.p.m. 
There ewe " cylinders each of bore 110 mm. The stroke is 120 mm. 
and each cylinder fires once in two revolutions. Find the average 
brake mean pressure (^P).t 

1:2. Air flows through an orifice from a reservoir in which the pres- 
sure is P lb. per sq. foot, and temperature T into a region of lower pres- 
sure, heat being neither received nor rejected during the operation. 
Obtain an expression for the ma x i m u m discharge in lb. per sec. in 
terms of P.. T. the rZr stive area of the orifice and the ratio of the specine 
hea: - Tripos, 1904.) 

* ": Z:: ;_ Mi p. 43. f ^epar. I 



CHAPTER IX 

Petrol Engine Efficiency arid Rating 

Efficiency Tests under Various Conditions — Effect of Cylin- 
der Dimensions on Power and Efficiency — Engine Rating 
— R.A.C. Rule — Callendar Rule — Operation of Two-Stroke 

Engine — Composition of Exhaust Gases as related to 
Efficiency — Motor Vehicle Tests. 

167. Efficiency Tests on Petrol Motors. — Some of the most 
searching tests that have been carried out on petrol motors 
have been those undertaken in the Engineering Laboratory at 
Cambridge under Professor Hopkinson. 

In one set of such tests * the engine used was a 16/20 H.P. 
Daimler four-cylinder engine capable of running at 250 to 
1,400 revs, per min. Other particulars were- — 

Total volume of one cylinder with 

piston on out centre . . 0-04 cu. ft. 

Volume of compression space . 0-0104 cu. ft. 
Compression ratio . . . 3-85 

Diameter of cylinder . . 3-56 inches = 90 mm. 

Length of stroke . . .5-11 inches = 130 mm. 

The indicator used was a reflecting one of the piston type. 

The tests involved three sets of measurements — (1) engine 
losses, (2) B.H.P., and (3) fuel consumption. From (1) and 
(2) the I. H.P. could be obtained, and therefore the mechanical 
efficiency. The tests were run with the carburettor as fitted 
by the engine builders, and it must not therefore be taken that 
the engine was of necessity adjusted to give maximum power 
or efficiency. 

* Engineering, February 8, 1907i 

277 



278 THE INTERNAL COMBUSTION ENGINE [chap, ix 

The results of the tests are shown in Fig. 99 in which curves 
are given for the I.H.P., B.H.P., the mean effective pressure 
and the torque on the crankshaft. The mechanical efficiency 
varied from 85 to 75 per cent. — falling slowly as the speed 
exceeded 600 revs, per min. The petrol used had a thermal 
efficiency on the lower scale of 17,000 B.Th.U. per lb., and 
on this basis the following table of thermal efficiencies was 
calculated — 



Speed 


Petrol Consumption (Pounds) 


Thermal Efficiency 


Revs, per 
Minute 


Per I.H.P. 
Hour 


Per B.H.P. 
Hour 


Per 1,000 
Revs. 


On 
I.H.P. 


On 
B.H.P. 


400 

400 

600 

600 

800 

1,000 

1,000 

1,100 

1,225 


0-78 
0-75 
0-685 
0-655 

0-6 

0-6" 

0-59 

(0-65) 


0-9 

0-87 
0-81 
0-77 

0-75 
0-75 

0-785 
0-94 


0-30 

0-28 

0-26 

0-24 

0-24 

0-22 

0-206 

0-202 

0-22 


18-6 
19-3 
121 

22 

24-2 
24-2 

24-6 
(22-3) 


161 
16-6 
17-9 
18-8 

19-3 i ' 
19-3 
18-4 
15-4 



Note. — At speeds 400, 600, and 1,000, two tests are given to show 
the range of variation. At 1,225 the indicated horse-power is uncer- 
tain, as no direct measurement of loss was made at that speed. 

The thermal efficiency rose considerably with increase of 
speed — due no doubt in part to there being less time for the 
explosive mixture to cool, but in view of the variability of the 
composition of mixture passed by the carburettor (of the usual 
jet type) it is not safe to build too much on these measurements. 
An interesting measurement in addition to the above was that 
of the pressure in the induction pipe. With the throttle wide 
open and a speed of 1,000 r.p.m. this pressure was about 1| 
lb. /in. 2 below atmospheric pressure. With the speed reduced 
to 400 r.p.m. this pressure was less than J lb. /in. 2 below atmo- 
sphere. The mean effective pressure (P) in the cylinder was 
at its maximum value of 88 lb. per sq. inch when the speed 
was 600 r.p.m. ; at this point the mechanical efficiency (rj) 
was 85 per cent., so that the product ??P was 75, The expres- 



chap, ix J PETROL ENGINE EFFICIENCY 



279 



sion ^P is in very common use in estimating the performance 
of petrol engines, and it is called the brake-mean-pressure. It 
is used in preference to P, the indicated mean effective pressure, 
because indicator diagrams of these engines are seldom taken 
{see Ch. V) . With more modern engines than the Daimler engine 
on which the above tests were made the value of r/P would 
usually be about 90 lb. per sq. inch, and although in ordinary 
touring car engines this value would not be sustained beyond 



HP 
24 



20 



;6 



12 



500 



Piston Speed 



1000 











































































/C 


I.H.P. 














*J> 


~ ^^~ 




















v^ 




























JorS. 


ii5— — 












































/C 


B.H.f 





























































































































































120 
110 
100 
90 
80 
70 
60 
50 
40 
30 
- 20 
10 



C/J 



ZOO 400 600 800 1000 

Revs, per Minute. 



1200 



1400 



Fig. 99. — Professor Hopkinson's tests on 1/20 H.P. Daimler Engine. 

about 1,200 r. p.m., in some special engines it is maintained till 
3,000 r.p.m. 

Tests * to discover the relation between the rate of con- 
sumption of petrol per B.H.P. and the character of the spark 
employed were undertaken at the City Guilds College by 
Messrs. Topham and Tisdall. A small single cylinder De Dion 



* Engineering, December 28, 1906. 



280 THE INTERNAL COMBUSTION ENGINE [chap, ix 

engine was used of 66 mm. bore, and 70 mm. stroke. The 
proportion of air to petrol varied with atmospheric conditions 
and was adjusted for each test so as to give a maximum 
power development, the throttle was kept fully open, and 
the air supply alone was varied. The engine was run at 
full normal speed. The chief results obtained were as 
follows — 



Source of Spark (high tension) 



Petrol Consumption in galls, per 
B.H.P. Hour 



Accumulator with no external gap . 
Magneto with external gap . 
Accumulator with external gap . 



0-208 to 0-187 
0-289 to 0-249 
0-226 to 0-24 



Not much can be gained from these measurements, though 
it would seem that different forms of high-tension ignition have 
a generally similar effect on the rate of fuel consumption, the 
accumulator having a slight advantage. The result of using 
an external spark gap in the high-tension circuit is worth 
recording. The plug insulation resistance was over 1,000 
megohms cold, but after being used for running the engine for 
five minutes, it fell to about 6 megohms. At a dull red the 
resistance fell further to 2 megohms, and eventually sparking 
ceased entirely. On the introduction of an external air gap 
in the circuit, however, sparking was resumed, even when the 
plug was made bright red hot, and the resistance had sunk as 
low as 800,000 ohms. The experimenters considered that this 
showed that leakage through the porcelain of the plug might 
become quite large enough to stop sparking entirely, and that 
the effect of the introduction of the external air gap was to 
prevent the application of the voltage across the sparking 
points until the instant at which current began to flow in the 
high-tension circuit, the spark then being of the nature of a 
condenser discharge, and the leakage being considerably 
reduced in quantity. 

168. The Effect of Cylinder Dimensions on Power and Effi- 
ciency,— Many attempts * have been made to produce a work- 



* Proc, I.A,E., 1907 and 1911. 



chap, ix] PETROL ENGINE EFFICIENCY 281 

ing theory of the effect of cylinder dimensions, particularly 

cylinder diameters, on the economy and power of internal 
combustion engines. Most of them have owed their origin to 
the competitive trials of motor cars in which the various vehi- 
cles are classed according to horse-power, and which therefore 
require that the figures given should be properly comparable. 
For large internal combustion engines the existence of such rules 
is not of vital importance, since the comparison of one engine 
and another depends upon so many other factors, and, more- 
over, organized competitions are unknow T n. 

The first attempt to deal with this matter on a scientific 
basis is due to Professor Callendar, who read a paper before 
the Institution of Automobile Engineers on " The Effect of 
Size on the Thermal Efficiency of Motors." Cylinders as 
large as 14 inches w T ere considered which, although common 
in gas engine practice, were well outside the range of motor 
car cylinders. This made the paper the more valuable in the 
general sense, although from the strictly motor car point of 
view advantage would have been gained had the theory been 
based entirely upon engine trials with cylinders nearer the 
customary motor car size. As it was, however, the paper 
presented a general theory not only applicable to motor cars 
but to larger engines also. 

It is well known that the " air standard " of efficiency is 
higher than the efficiencies obtained in practice, and that the 
ratio of the latter to the former is commonly about 60 per cent. 
This means a deficit of 40 per cent, owing to some cause or 
other. What is this cause ? The answer is, first, that the 
' air standard " of efficiency is a far higher one than any actual 
engine can ever achieve, owing to the fact that whereas the 
value of y assumed in the " air standard " equation is 1-40, its 
average value for the actual cylinder gases at working tem- 
peratures, taking the increase of specific heat into account, 
Avould be more nearly 1-3.* This alone accounts for about 20 
per cent, of the 40 per cent, apparently lost, and the remaining 
20 per cent, is due to various heat losses such as jacket loss, 
radiation loss, etc. In general, therefore, it would appear 

* £>ee par. 66, 



282 THE INTERNAL COMBUSTION EXGIXE [chap, ix 

that the 40 per cent, loss is divided about equally between the 
two. thoughin Professor Callendar's view it would be more correct 
to put the unavoidable apparent loss due to the properties of the 
gases down as 25 per cent., and the remaining 15 per cent, to 
the loss of efficiency owing to heat losses during the operations 
of the cycle. It is clear that, as the volume of gas in a cylinder 
will be proportional to the cube of the dimensions, and the 
surface of the cooling walls proportional only to the square of 
the dimensions, doubling the size of an engine will halve the 
heat losses due to surface cooling. The fact that the larger 
engine will probably not run at so high a speed has little effect 
on this conclusion, as although the time the gases will have to 
cool will increase with diminishing speed, yet the diminished 
speed will lead to diminished scrubbing of the cylinder walls 
by the molecules of the gases, and so leave matters much where 
they were. It may therefore be estimated that the loss of 

efficiency due to surf ace coolino- will be x — where D is the 

cylinder diameter. Some losses, however, such as the radiation 
loss, do not follow this law of dimensions, though what law they 
do follow it is not yet known. Still, one of the most important 

losses has been shown to be proportional to -— , and as an 

attempt at a working theory, there is no harm in grouping the 

losses together and putting them proportional to — — . This is 

what Professor Callendar does with several sets of engine trials. 
One set is based on his own experiments on an engine with a 
cylinder diameter of 2-36 inches, and the others are drawn from 
the Report of a Committee of the Institution of Civil Engineers. 
From the combined results on all four engines as given below, 
he finds that the value of the constant a to be put in the 
expression — 

loss of efficiency ==— 

actually comes out as 1-0 when D is measured in inches. So 
that loss of efficiency =— -. 



chap, ix] PKTROL ENGINE EFFICIENCY 



283 



Designation of engine .... 
Diameter of cylinder, inches 


C 
2-36 


L 
5-5 


R 

90 


X 

140 


Loss of efficiency ( = ,^ J 


0-42 


018 


0-11 


0-07 


Resulting efficiency figure (l — j) J 


0-58 


0-82 


0-89 


0-93 


Observed relative efficiency as com- 
pared with air standard . 
Ratio of last two lines .... 


0-44 
0-76 


0-61 
0-75 


0-65 
0-73 


0-69 

0-74 



It appears that the value of the above constant a, viz. 1-0, 
was chosen so as to render consistent the figures in the last 
line of the above table. 

In this way the relative efficiency of any engine is written 

down as 0-75 (l — J and if the " air standard " efficiency 

for the degree of compression under consideration be called 
E, then the 

thermal efficiency = 0-75E( 1 — — 

Had the '* air standard " been a standard really applicable 
directly to gas engines, the figure 0-75 would have been unity, 
so further simplifying the formula. As it is the above equa- 
tion shows that even the largest engines cannot get nearer the 
: ' air standard " than 75 per cent. It is useful to compare this 
conclusion with the values found in par. 65. Callendar uses 
these results in obtaining his P.C. method of rating, to be 
described in par. 170. Before coming to that, however, it 
is necessary to consider the simpler R.A.C. rating. 

169. R.A.C. Rating. — The rating recommended by the 
R.A.C, and adopted by the Treasury, is that originally sug- 
gested by Dugald Clerk, who proposed 

rated H.P. =nd 2 ^r2-5 

where n is the number of cylinders and d the cylinder diameter 
in inches. Thus a four-cylinder engine of 4 inch bore would 
have a rated H.P. of 25-6. 

This rating is tantamount to assuming that for a given mean 
pressure in the cylinder the piston speed in feet per minute 



S 1 THE INTERNAL COMBUSTION ENGINE [crap, ix 

will be the same for all types and sizes of engine. Experiment 
has shown that the mean pressure is practically independent 
of bore and stroke, but there is uncertainty how far it is safe 
to assume that the piston speed is the same in all engii 
This uncertainty is due to lack of clearness as to what the rated 
H.P. is supposed to represent. It might be any one of thes-? — 

(1) Ma x imum H.P. on the bench when running '* all out." 

(2) Ma x i m um H.P. on level road when running " all out/' 

(3) Max im um H.P. when climbing the steepest. hill climbable, 

or 

(4) Average H.P. when running on roads in normal unim- 

peded service. 

Now for (1) the B.A.C. rating method is probably the most 
correct, using, however, a lower constant than 2-b. Eor {2) 
the engine speed in r.p.m.. and not the piston speed, is the 
more nearly constant factor, and H.P. is therefore roughly 
proportional to cylinder volume, and is approximately = volume 
in cu. cms. — 100. Eor (3) the engine speed is commonly in 
the neighbourhood of BOO or 1.000 r.p.m.. and the volumetric 
rating therefore applies here also, and we may roughly say 
H.P. — volume in cu. cms. -j- 130. 

For (4) there is little data available, but the E.A.O. formula 
probably fits it very nearly with the present constant. We 
may therefore make out the following table : — = ' :>ta! 
displacement volume in cu. cms.) 

(1) Maximum bench H.P.=£m? 2 where k is some constant 
( (2) Max. H.P. on road=C — 100 
- (3) Max. H.P. on hill =C — 130 

I (4) Average H.P. normal uninterrupted service on road- = 
nd 2 — 2-d. 

170. The Callendar Formula. — The B.A.C. rating assumes 
that all sizes of engines are equally mechanically efficient when 
worked under the same conditions, which is not the case. If 

D 2 be multiplied by the expression ll — — j as proportional 

to the mechanical efficiency, the result is to obtain the exp: 
si on I)(D — 1 ) which should be used in place of P 2 in 1 



chap, rx] PETROL ENGINE EFFICIENCY 



285 



rating formula. In this way Professor Callendar suggests a 
" P.C. rating " (Petrol Consumption rating) of 

B.H.P.— D (D— 1) 

the figure 2 being the suitable constant. The P.C. ratings 
and R.A.C. ratings for a number of cylinder diameters are 
given in the following table — 



D 


R.A.C. Rating 


P.C. Rating 




(per cylinder) 


(per cylinder) 


Inches 


B.H.P. 


B.H.P. 


1 


0-40 


nil 


2 


1-6 


1-0 


3 


3-6 


30 


4 


6-4 


60 


5 


10-0 


10-0 


6 


14-4 


150 


8 


25-6 


28-0 


10 


40-0 


450 


20 


160 


190 



These two formulae are shown plotted in Fig. 100. The 



■1) gives the H.P. per cylinder. 



Callendar formula — (D 

2 

The result of using the P.C. rating would be, to quote Pro- 
fessor Callendar : — " According to the R.A.C. formula, a four- 
cylinder engine with 2 in. bore and stroke (like the F.N. 
motor cycle engine) is rated at 6-4 H.P., and is equivalent to 
a single-cylinder of 4 in. bore. According to my experi- 
ments the four-cylinder of 2 in. bore could not develop much 
more than 4 H.P. under ordinary conditions, and would stand 
no chance against the single-cylinder of 4 in. bore. A 
four-cylinder of 3 in. bore is equivalent to a single- cylinder of 
6 in. bore by the A.C. rating, but according to the P.C. rating, 
the single-cylinder would have an advantage in point of power 
of 25 per cent. A two- cylinder of equal power on the A.C. 
rating would have an advantage of about 12 per cent, over 
the four-cylinder, and a six-cylinder a disadvantage of about 
10 per cent." Professor Callendar also remarks : — " An obvi- 



286 THE INTERNAL COMBUSTION ENGINE [chap, tx 



S 


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chap, ix] PETROL ENGINE EFFICIENCY 287 

ous objection to the P.C. type of formula is that the B.H.P. of 
an engine of 1 in. bore and stroke would be zero. According 
to the R.A.C. rating it should be '■= H.P. It would no doubt 
be possible to get such an engine to run if very delicately made, 
but the effect of ignition lag would be serious at the normal 
speed of 6,000 revolutions per minute, and I doubt whether 
it could be made to give as much as ^ H.P. on the brake." 

At the present time there are few motor car engines that 
could not yield, without pressing, an amount of power given 
say by such a formula as : — 

H p _ KD(I)+S) 
5 

where N and D are as before and S is the length of the stroke 
in inches. If in a given engine the length of stroke be 10 per 
cent, greater than the diameter of the bore, this formula would 
attribute to the engine a H.P. greater by 5 per cent, than one 
in which stroke was equal to the bore. Whether the full 
engine H.P. can be utilized when the engine has been fitted to 
a motor car depends upon whether the gear-ratios have been 
suitably chosen. 

None of these formulae apply to anything but four-stroke 
single-acting engines. Some motor cars, however, have two- 
stroke single-acting engines, and for them the rating is low. 
A two-stroke engine can give, on the bench, about 60 per cent, 
more power than a four-stroke engine of the same bore, stroke 
and number of cylinders. The reason why two-stroke engines 
do not give twice as much as four-stroke engines is that the 
compression and explosion pressures are usually less, and there 
is often a considerable amount of fuel which escapes unburnt. 
When a two-stroke engine is fitted to a car a difficulty arises 
owing to its very powerful and noisy exhaust, the effective 
silencing of which increases the back pressure and largely 
neutralizes the gain of power there would otherwise be over 
the four-stroke engine. 

171. Ratio of Power to Weight. — An interesting point is to 
find out what is the best cylinder diameter for minimum weight 
of engine per B.H.P. developed. 

If the weight oo D 2 ' 5 and the H.P. 8 D(D — 1) 



288 THE INTERNAL COMBUSTION ENGINE [chap, ix 

Then H.P. D(D— 1) D— 1 , . , 

= — -— — which 

weight D 2 - 5 D 1 - 5 

gives the following table : — 

D :— 1 2 3 4 5 

-^:— 0-353 0-385 0-375 0-357 

showing that the greatest H.P. per lb. weight of motor would 
be obtained when D = 3 inches, although D = 4 inches gives 
practically as good a result. The weight will however be 
affected also by change in the compression ratio since with in- 
creasing compression the engine parts must be made heavier. 

172. Operation of Two-Stroke Engines. — Although the two- 
stroke petrol engine has twice the number of working strokes, 
per 1,000 r.p.m., that a four-stroke engine has, it suffers much 
from loss of power owing to some of the entering charge passing 
out of the exhaust before it has been burnt. Also the exhaust 
valve has to be opened before the end of the working stroke, 
and this diminishes the effectiveness of that stroke. 

Careful experiments on two-stroke engines have been carried 
out by Watson and Fenning.* The engine tested was a single 
cylinder Day engine rated at 2 J H.P. at 900 r.p.m., the cylinder 
bore and stroke being 3J- in. When under test the power was 
absorbed electrically and the I. H.P. was measured by a reflect- 
ing indicator. Tests were made at 600, 900, 1,200 and 1,500 
r.p.m. 

The results are given in the following table (see next page). 

The best values of P were obtained when the ratio of air to 

petrol by weight was 12 to 1, and the following were the 

figures : — Speed P 

r.p.m. lb. per sq. in. 

600 63 

900 58 

1200 53 

1500 48 

These figures show how at high speeds there is not time for a 
full charge to enter the cylinder ; also that ^P would not be 
much more than half the value usual with four-stroke engines. 

* Proc. I.A.E., 1908 and later. 



chap, ix] PETROL ENGINE EFFICIENCY 



289 



Spe^d 
R.P.M. 



636 

596 

638 

609 

601 

604 

897 

903 

902 

898 

938 

905 

900 

937 

907 

897 

1209 

1206 

1199 

1218 

1212 

1210 

1218 

1504 

1514 

1510 

1509 

1502 

1500 

1509 

1510 

1510 

1508 

1508 

1501 



I.H.P. 



2-71 
2-51 
2-73 
2-48 
2-35 
•36 
•51 
•60 
■59 
•55 
•68 
•54 
•57 
3-55 
3-30 
3-26 
412 
4-23 
4-34 
4-29 
4-29 
3-77 
3-79 
4-85 
4-71 
4-75 
4-80 
4-94 
4-80 
4-77 
4-82 
4-82 
4-91 
4-51 
4-52 



B.H.P. 



21 
1-9 
21 

1-9 
1-7 
1-7 
2-8 
2-8 
2-8 
2-8 
2-9 
2-8 
2-8 
2-8 
2-5 
2-5 
31 
3-3 
3-4 
3-3 
3-3 
2-8 
2-8 
3-6 
3-4 
3-5 
3-5 
3-7 
3-5 
3-5 
3-5 
3-5 
3-6 
3-2 
3-3 



Lb. of 
Petrol 
per 
1,000 
revs. 



•0651 
•0660 
•0592 
•0531 
•0493 
•0493 
•0650 
•0612 
•0579 
•0579 
•0520 
•0541 
•0493 
•0452 
•0425 
•0426 
•0564 
•0561 
•0567 
•0498 
•0396 
•0333 
•0331 
•0449 
•0428 
•0424 
•0398 
•0392 
•0375 
•0369 
•0342 
•0327 
•0325 
•0304 
•0307 



Lb. of j Ther- 
Petrol ' mal 
per | Effi- 
I.H.P. ciency, 
hour Gross 



•917 
•941 
•830 
•784 
•756 
•758 
•997 
•923 
•873 
•881 
•795 
•831 
•746 
•716 
•702 
•703 
•992 
•960 
•945 
•847 
•671 
•641 
•637 
•838 
•825 
•808 
•751 
•716 
•703- 
•700 
•643 
•614 
•598 
•610 
•610 



149 
145 
165 
174 
181 
180 
137 
148 
157 
155 
172 
165 
183 
191 
195 
194 
138 
143 
145 
161 
204 
213 
215 
163 
166 
169 
182 
191 
195 
195 
213 
223 
229 
224 
224 



Ther- 
mal 
Effi- 

ciency, 

Net. 



•230 
•226 
•252 

•268 
•279 

•278 

•212 
•217 

•247 



•270 
•276 

•169 
•177 
•175 
•201 
•250 
•262 
•264 
■179 
■177 



•206 

•208 



•247 




59 

57 

57 

57 

58 

58 

58-0 

57-7 

57-4 

58-2 

55-6 

53-4 

53-4 

501 

51-6 

52-8 

51-8 

52-0 

45-8 

45-7 

47-2 

45-7 

46-2 

46-7 

48-3 

470 

46-5 

46-9 

47-0 

47-9 

43-9 

44-3 



Throttle Valve partly closed 



11-24 
11-48 
12-45 
13-88 
1512 
1518 
9-86 
10-35 
10-91 
1105 
11-76 
11-83 
1302 
13-57 
14-86 
15-31 
9-75 
9-91 
9-92 
10-96 
13-87 
16-74 
16-89 
1006 
10-43 
10-68 
11-29 
11-61 
1212 
1218 
1310 
13-71 
13-98 
14-75 
14-85 



639 


2-25 


— 


•0486 


•828 


•165 


•216 


51-7 


1212 


897 


2-86 




•0415 


•781 


•175 


•187 


46-9 


11-27 


896 


2-89 




•0416 


•775 


•177 


•199 


47-4 


11-36 


1208 


3-55 




•0339 


•693 


•197 


•213 


431 


11-73 


1510 


3-65 


— 


•0269 


•669 


•204 


•209 


35-5 


12-27 



30 



18 
19 
17 
20 



25 

6 

11 

7 
2 



u 



290 THE INTERNAL COMBUSTION ENGINE [chap, ix 

173. Composition of Exhaust Gases. — The efficiency of a 
petrol engine naturally depends on the degree to which com- 
bustion is complete. The exhaust gases should not. for good 
efficiency, contain any CO. All the carbon present should be 
burnt to C0 2 . Nor. if the proportion of ah is closely adjusted, 
will there be any oxygen in the exhaust. 

It is difficult to write down the chemical formula in accord- 
ance with which the combustion of petrol takes place in an 
atmosphere of ah. owing to the complex nature of the petrol 
molecule, but it is interesting to write down the combustion 
equation for C 8 H , 8 . and to look upon it as representing, approxi- 
mately, what occurs with petrol. 

C 8 H U burns with 2 as follows — 

2C 5 H 1S — 250 2 = 16CO a — 1SH 2 

so that 2 7 volumes of mixture give 34 volumes of products, 
or. if the steam be condensed to water. 16 volumes. 

In actual working, ordinary air and not pure oxygen is used., 
so that there is nitrogen also to be considered. With 25 
volumes of oxygen. 94 volumes of nitrogen would be associated 
— making a total of 119 volumes of air. Each volume of this 
petrol therefore requires 60 volumes of air for complete com- 
bustion, and the equation can be therefore rewritten as — 

2C 5 H 15 — 250, — 94N 2 = 16C0 2 — 18H 2 — 94N 2 . 
The right-hand side of this equation is exhaust products, and 
the composition by volume will be — if the volume of the water 

be neglected — or 14-5 per cent, of CO, and 85-5 per cent. 

110 r " ^ 

of N 2 . If too little ah were admitted some of the C0 2 would 
be reduced to CO. which being a poisonous gas is a very un- 
desirable element in the exhaust : moreover, it would reduce 
the thermal value of the gas owing to a part of the carbon not 
being completely oxidized — a loss which has already been dealt 
with quantitatively in the chapter on suction producer gas. 
If too much air is admitted, free oxygen will appear in the 
exhaust. We have therefore the following three rules : — 

(1) When oxygen occurs in the exhaust too much air has 

been admitted. 
2 Too little air leads to formation of CO, 



chap. ix] PETROL ENGINE EFFICIENCY 



291 



(3) When neither CO nor 2 appear in the exhaust the air 
is in the right proportion. 

Some experiments on the composition of exhaust gases were 
made by Professor Hopkinson and L. G. Morse, in the engineer- 
ing laboratories at Cambridge, on the Daimler engine already 
referred to. 

The speed Avas kept at 700/750 r.p.m., and a jet carbur- 
ettor of the usual sort was used. The throttle was kept open 
so that the suction never exceeded J lb. per sq. inch in the 
inlet pipe close to the inlet valves. Fuel used was Pratt's 
motor spirit ; density 0-715 to 0-720 ; Calorific value 18,900 
B.Th.U. (lower value). The exhaust gases were analysed by 
the ordinary volumetric methods, the C0 2 being absorbed by 
potash, the oxygen by pyrogallol, the CO by an acid solution 
of cuprous chloride, and the H 2 by palladianized asbestos. 

The following table shows the results recorded — 



Experiments made by Professor Hopkinson 


and L. G. Morse. 


Petrol consumption in lb. 














per 1,000 revs. . 


0181 


0191 


0197 


0-217 


0-250 


0-293 


Brake load at 43 in. radius 














lb. 


25 


27-5 


29-3 


29-4 


29-3 


27 


Thermal efficiency 


0-244 


0-252 


0-261 


0-238 


0-204 


0162 


C0 2 — measured 


10-9 


12-8 


13-5 


10-6 


9-6 


6 


2 „ ... 


3-6 


1-5 


0-2 


— 


— ■ 


— 


CO „ ... 


— 


— ■ 


0-7 


5 


6-25 


11-6 


H 2 ,, ... 


— 


— 


— ■ 


21 


2-65 


8-7 


N 2 by difference . 


84 


84 


84 


81 


80 


73 


Total 2 , calculated from 














N 2 


22-4 


22-4 


22-4 


21-5 


21-3 


19-4 


H 2 calculated 


15-8 


16-2 


16-8 


16-8 


17-2 


15-2 



From this it will be seen that when the CO and 2 are at 
a minimum, the C0 2 is 13-5 per cent, and the N 2 84 per cent., 
figures which are very close to those calculated above from 
the approximate chemical formula. Moreover, it will be seen 
that it is at this point that the highest thermal efficiency 
(0-261) was recorded. This is best brought out when the 
points are plotted in a curve, as in Fig. 101. 

Curve B (thermal efficiency) shows how quickly the thermal 
efficiency declines when CO begins to be produced. Curve A 



292 THE INTERNAL COMBUSTION ENGINE [chap, ix 

(corresponding to B.H.P.) is of a very different form, as 
although it is true that minimum production of CO corresponds 
to an output in H.P. very little less than the maximum, yet 
that maximum is found when the CO amounts to 0-7 per cent. 
and is very nearly maintained even when the proportion of CO 
rises to over 6 per cent. The ideal condition of working is 




01& 



018 0-20 0-22 0-24 0-26 
Petrol Consumption 

Fig. 101. 



02B 



0-30 



obviously the apex of Curve B, but the corresponding point 
on Curve A is not a convenient one to work at. In all engineer- 
ing work it is customary to work, if possible, near to the 
middle of a curve which has a slow hump, such as Curve A. 
in order that small variations to right or left may not make 
much difference. The ideal working point on Curve A is 



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294 THE INTERNAL COMBUSTION ENGINE [chap, ix 

therefore by no means the most convenient practical point, 
which in this case would correspond to about 5 per cent, of 
CO. This temptation has led engine builders to set carburettors 
so to give maximum power, instead of aiming at minimum 
production of CO and therefore maximum thermal efficiency. 
Dugald Clerk has also carried out tests of this kind. He 
used for this purpose the engine on a 18 H.P. Siddeley car. 
The engine was a 4-cylinder one, bore 4 inches, stroke 4 inches. 
Samples of the exhaust were taken while- — 

(a) The car was standing on the level with the engine 

running as slowly as possible. 

(b) The car still standing, but engine running at about 

600 r.p.m. 

(c) The car running on a level at about 18 m.p.h., the 

throttle less than half open. 

(d) The car climbing a hill, engine running about 1,000 

r.p.m., and throttle from three-quarters to full open. 

It will be seen from the above table that under circum- 
stances which might quite often occur in practice about 4 
per cent, of CO is being produced. To meet the difficulties 
of designing a carburettor which should mix air and petrol 
in constant proportions under all conditions of load and speed 
is no easy thing, indeed most builders aim at quite different 
mixtures, viz., those that make for ease at starting, for 
rapidity of " picking up," and other features of car manage- 
ment that make for ease of manipulation. 

Dugald Clerk concludes from the results of his experiments 
that the following conditions appear to produce imperfect 
combustion — 

1. Too rich mixture with insufficiency of oxygen. 

2. Too weak mixture with excess of oxygen, but too slow 

a rate of ignition and combustion. 

3. Irregular mixture — mixture supplied too rich in com- 

position at one part of the stroke, and too weak in 
another ; that is, bad mixture. 

4. Engine and carburettor cold. This tends to cause im- 

perfect combustion, due partly to low temperature 
and partly to bad carburetting. 



chap, ix] PETROL ENGINE EFFICIENCY 295 

5. Improper timing of ignition, and missed ignitions. 

6. Igniting in the body of the cylinder, instead of in a 
port. This is liable to produce imperfect combustion at light 
loads. 

The sixth of the above conditions is an exceptionally inter- 
esting one. It seems incontestably to be the case that the 
presence of ;; pockets " in cylinders leads to loss of efficiency, 
' pockets " being the name given to any recess in the top of a 
cylinder which has the effect of increasing the clearance volume. 
But it is almost equally certain that the presence of " pockets ,: 
improves the running of the engine under working conditions : 
and renders it, as it is termed, " more flexible." Pockets 
lower the efficiency, as they increase the ratio of surface to 
volume, but they render ignition more certain, as, even at 
light loads when the exhaust products left in the clearance 
space dilute the incoming charge very considerably, there is 
the likelihood of the neighbourhood of the sparking plug 
(which is probably situated in or near one of these pockets) 
being rich locally in explosive mixture, so ensuring the proper 
starting and timing of the ignition. Too much " pocketing " 
on the other hand may lead to detonation of the charge. 

174. Tests on the Road. — Not only are petrol engines for 
motor vehicles tested on the bench, but also when fitted 
into their chassis. Such tests are kept as closely as possible 
to normal working conditions. Measurements of speed and 
H.P. are needed, also wherever possible tests of acceleration 
and of hill-climbing ability. To measure the B.H.P. on the 
road it is necessary to know the speed and the resistance to 
motion (R) in pounds per ton. 

Then 

-d tt p Velocity in m.p.h. X R X weight of car in tons 
' 375 

The speed is usually read ona" speedometer " and the resis- 
tance by an " accelerometer." Such an accelerometer is 
shown in Fig. 102. Its action * is that of weighing the forces 

* For a description of the mechanism, and of tests made with it, see 
The Engineer, September 16, 1910, and Proz. I.C.E., Vol. 188 ; also 
Application of Power to Road Transport (Constable & Co.). 



_ i THE INTERNAL COMBUSTION ENGINE [chap, ix 

which oppose the motion of the car. and the needle points to the 
figure on the scale showing the number of " pounds per ton " 
of resistance at any moment. Such devices are called acceler- 
ometers because they were first introduced for the measure- 
ment of train acceleration. They can however be used for 
other purposes. 

175. Fuel Consumption Tests.- — It is also usual to measure 
the amount of fuel used on a road-test, and to put the result 




Fig. 102. — Accelerometer. 



into the form " gross-ton-mi les-per-gallon " of fuel. i.e.. the 
product of miles rim per gallon by the total moving weight 
in tons. This figure affords a useful comparison of car with 
car provided that care is taken to measure during the run the 
average amount of the resistance overcome by the method 
described in the previous paragraph. This is necessary, as 
with heavy vehicles the resistance is sometimes twice as high 
on winter roads as on summer ones, and the " gross-ton- 
mi les-per-gallon ** figures will be changed in proportion. It 
is best to express the relationship in the form " gross-ton- 
miles-per-gallon on roads of normal road resistance/' and to 



chap, ix] PETROL ENGINE EFFICIENCY 



297 



take 70 lb. per ton as a common standard of resistance. This 
brings all such tests to the same basis of comparison. Not 
only does the state of the roads affect the resistance, but the 
speed at which the car runs during the trial also affects it con- 
siderably. At high speeds the component of the resisting 
force due to air resistance is very greatly increased. On good 
roads the total resistance with the average four^seated touring 
car * is usually about 

R. in lb. /ton =50 + 0-06V 2 where V is in m.p.h. 
For a typical motor wagon under the same conditions 

R = 50 +010V 2 

but much depends in either case on the form of the body of 
the vehicle, and experiment is the only safe guide. 

176. Windage Experiments. — S. F. Edge once carried out 
tests at Brooklands to see what effect the raising of a large 
wind screen would have on the speed of a large Napier car 
(38-4 H.P. R.A.C. rating). His results were — 



Area of Wind Resistance Screen 
in Square Feet 


Speed in M.P.H. 




30 


47-85 




28 


500 




26 


52-9 




24 


56- 15 




22 


54-0 




20 


55-5 




18 


57-0 




16 


57-6 




14 


600 




12 


62-5] 




10 


64-2,^ 




8 


6615 




6 


70-25 




4 


75:0 




2 


73-8 







790 





These figures are shown plotted in Fig. 103. Students will 
find it interesting to estimate what the resistance law must 
have been to give these results. 

* Vide Application of Power to Road Transport (Constable & Co.). 



29S THE INTERNAL COMBUSTION ENGINE [chap, ix 



•no 






























40 






V 

\ i 




































e 


















, 
















e 




















\p 
















<4 

1 

«f 30 
u 

t: 

a 

•a 

9: 




















; i 
















•> \^ 




























»\ 
















- 


















x 


















^ 20 


















^S 






















































"0 

1 




























's. ' 


' 






























B 


































































°0£ 


serif 


ed 1 


'alue 


s 










5 


















































































































40 



45 



55 60 G5 70 75 

Sp eed in Miles per Hour. 



so 



es 



Fig. 103. — Diagram showing the effect of wind resistance on speed, as found 
by Mr. Edge on a Napier car carrying a special wind screen. 



177. Hill Climbing Tests. — The initial acceleration with 
which a car can start to move on a level road is closely con- 
nected with the steepness of the hill it can climb. If a be the 
angle of the steepest hill clhnbable. then the equivalent accele- 
ration is g sin a. This is obvious, as the same engine effort is 
needed to climb a hill of this slope as to give an acceleration 
equal to g sin a. Change of gear affects hill climbing ability 
in the manner illustrated in Fig. 104. The lower continuous 
curve is the resistance curve, whilst the continuous curve 
crossing it is the engine torque curve (on top gear) plotted to 



(hap. ix] PETROL ENGINE EFFICIENCY 



299 



the same scale, i.e., so that both show the equivalent tractive 
effort at the rear road wheels. The two dotted curves parallel 
to the resistance curve are the curves of resistance when 
ascending gradients of 1 in 20 or 1 in 12 respectively, since 
the} 7 represent the result of adding the extra effort necessary 
for hill climbing to that needed to overcome the resistance on 
the level. The upper dotted torque curve is that corresponding 
to the engine being on the next lower gear. 

These curves show that on a level road the tractive effort 




Torque on 
yh gear 



I'O 20 

Spsed in M.P.H. 

Fig. 104. — Tractive Effort and Resistance of a 15 H.P. motor car at various 

speeds. 



and the resistance will be exactly balanced at 34 m.p.h. If 
the road began to ascend, the resistance curve would rise 
bodily upwards, keeping parallel to itself, and the crossing 
point of the two curves would move nearer in showing a lower 
speed of travel. At the crest of the torque curve the motion 
becomes unstable, and the engine will stop unless the " gear ' : 
be changed. This point evidently comes just after the slope 
rises to a steepness of 1 in 20. On the lower gear the point of 
instability comes soon after the slope exceeds a 1 in 12 gra- 
dient. These torque curves correspond to the throttle 
being wide open. If, however, the vehicle were travelling on 



300 THE INTERNAL COMBUSTION ENGINE [chap, ix 

a level road on top gear at 20 m.p.h. and the throttle were 

suddenly opened wide, it will be seen that the engine would 

then be giving much more than twice the effort necessary to 

overcome the road resistance, and the balance would go to 

accelerate the motion of the car. In this particular case the 

excess effort is about 105 lb. per ton, and a force of 105 lb. 

acting on a mass weighing a ton would produce an acceleration 

105 X 32 
of = 1-5 ft. per sec. per sec, which would, therefore, 

be the acceleration of the car at this point. It is by drawing 
curves of this kind that it is possible to design the best gear 
ratios of mechanically propelled vehicles. 

178. R.A.C. Tests. — Interesting trials of touring vehicles 
and motor wagons have been organized by the Royal Auto- 
mobile Club, and from some of their reports the following 
tables have been made out— 



1907 Trials of Motor Wagons 


Net Load carried 


Average provided 

H.P. (R.A.C.) per ton of 

Gross Moving Load 


Average G.T.M. per 
Gallon of Petrol 


\ ton (5 cars) . 

1 ton (4 cars) . 
\\ tons (5 cars) 

2 tons (7 cars). 

3 tons (15 cars) 
5 tons (1 car) . 


7-82 

6-8 

7-24 

4-96 

501 

4-87 


27-4 

33-26 

30-9 

34-93 

40-6 

33-9 



R.A.C. International Touring Car Trials, 1908 



H.P. (R.A.C. rating) 


Miles run per 

gallon (average of 

best cars) 


Average weight 
(loaded) of best 
cars. Tons 


Gross-Ton-Miles 
per gallon of petrol. 
Average for best 
cars 


Up to 20 H.P. . 
20 to 40 H.P.. . 
40 to 60 H.P.. . 


24-2 
17-2 
15-9 


1-30 
1-72 
214 


30-7 
29-6 
33-9 



Note. — Total distance run in the 1908 trials was 1,977 miles on the 
roads in Scotland and England. Average speed of all cars probably 
between 15 and 20 miles per hour. 



chap, ix] PETROL ENGINE EFFICIENCY 301 

These results, taken into consideration with many later ones 
the author has collected, suggest the figure of 50 gross ton 
miles per gallon as a convenient standard of performance 
when reduced to the common basis of a tractive resistance of 
70 lb. per ton. This subject, however, needs a chapter to itself, 
and it is treated in fuller detail than is here possible in "The 
Application of Power to Road Transport." 

EXAMPLES 

1. Find estimates for the B.H.P. of the following cars, first on the 

,D 2 N , . , , ND(D+S) 

H.A.C. rating of — — , secondly using the formula - — — — , D and 
— ■ o o 

S being the diameter of bore and stroke respectively, both in inches. 

(i) 6-cylinder ; 5-inch bore by 7 -inch stroke, 

(ii) 4-cylinder ; 4-inch bore by 8-inch stroke, 

(iii) 4-cylinder ; 3^-inch bore by 4^-inch stroke, 

(iv) 2-cy Under ; 80 mm. bore by 280 mm. stroke. 

2. If the B.H.P. of an internal combustion engine (four-stroke single- 

D(D -1- S^ 

acting, one cylinder) be expressed by the formula — — -, calculate 

5 

the mean effective pressures which the formula assumes for the follow- 
ing mean piston speeds : — 1,000, 1,250, and 1,500 ft. per min. of an 

S 
engine having a stroke-bore ratio =— ■ of 1-50, and a mechanical efficiency 

of 0-80. 



ESSAY QUESTIONS 

[The following questions are, for the most part, selected from ex- 
amination papers.] 

1. Explain what is meant by (i) absolute temperature, (ii) a perfect 
gas. State the two chief laws which perfect gases obey, and prove 

PV . 

that for a perfect gas — is constant. 

2. What is the law connecting the pressure (lb. per sq. ft.), volume 
(cu. ft.) and absolute temperature (centigrade scale) of 1 lb. of air ? 
[One cu. ft. of air at N.T.P. weighs 0-0807 lb.] Explain why the speci- 
fic heat of a gas at constant pressure must be greater than the specific 
heat at constant volume. 

3. A gas expands so that PV re = constant. Show that if n is the 
ratio of specific heat at constant pressure to specific heat at constant 
volume, the expansion is adiabatic. (Mech. Sc. Tripos, 1898.) 






302 THE INTERNAL COMBUSTION ENGINE [chap, ix 

4. A gas engine works on an ideal cycle with adiabatic compression 
and expansion, receiving and rejecting heat only at constant volume. 
Obtain the expression of its efficiency. (Mech. Sc. Tripos, 1906.) 

5. In what way does the PV diagram of the ideal cycle for a gas 
engine differ from reality ? If it differs greatly, why are such calcula- 
tions of any use ? (B. of E., 1906.) 

6. Describe with sketches the mode of operation of an Internal Com- 
bustion Engine. Explain why, in general, such an engine is more 
efficient as a heat engine than a steam engine of the same power. 
State where the various losses of energy occur. A gas engine of 10 
B.H.P. consumes 180 cu. ft. of gas per hour, the calorific value of 
which is 690 B.Th. XL's per cu. ft. Find the total efficiency, and give a 
rough estimate of the different proportions of energy lost due to the 
causes mentioned above. (Mech. Sc. Tripos, 1906.) 

7. Describe a gas engine, and explain how it uses the Otto cycle 
of operations. Sketch the cylinder, showing piston, water-jacket, 
valves, shape of clearance space, and shape of exhaust outside the 
cylinder. (B. of E., 1899.) 

8. What is meant by " scavenging " in relation to gas engines ? 
How is it done, and how (or why) does it affect the efficiency ? 

(Mech. Sc. Tripos, 1898.) 

9. If the ideal P-V diagram of a gas engine consists of an area en- 
closed by two lines of constant volume intersected by two adiabatic lines, 
show that the efficiency of the cycle represented by the diagram de- 
pends on the compression ratio only, assuming that the specific heats 
of the working agent at constant pressure and also at constant volume, 
are constant. (B. of E., 1912.) 

10. Explain why the efficiency of a gas engine falls short of the 

, . / l \y~ 1 

ideal value obtained by substituting y=l-4 in the formula 1 — ( — ) 

Indicate the relative importance of the different reasons. 

(Mech. Sc. Tripos, 1913.) 

11. Criticise the Otto cycle from the point of view of (1) efficiency, 
(2) relation of power to weight on the part of the engine. In modern 
practice the tendency is to compress the mixture highly before ignition. 
How does this affect the points of your criticism ? 

12. How are Indicator-Diagrams taken from a petrol engine going 
at, say, 2,000 revs, per rnin ? Describe the Indicator. 

(B. of E., 1911.) 

13. Sketch the form of Indicator-Diagram you would expect to 
obtain from a petrol engine. Sketch diagrams showing : — 

(a) The spark too much advanced. 

(b) The spark insufficiently advanced. (B. of E., 1912.) 

14. What ought to be the composition of the exhaust gases from a 
gas engine using good coal gas or from a petrol engine ? Why does 
the actual composition differ from this ? (B. of E., 1910.) 



chap, ix] PETROL ENGINE EFFICIENCY 303 

15. Make a careful sketch of a petrol motor. Show a carburettor 
to an enlarged scale and explain the principle of its action. 

(B. of E., 1913.) 

1(>. In a gas-engine diagram the expansion curve usually lies above 
the " adiabatic " expansion curve, showing that, if the working sub- 
stance be a perfect gas, it must be receiving heat during the expansion ; 
yet. in fact, much heat is withdrawn from the cylinder walls by the 
cooling water. What do you regard as the most probable explana- 
tion of this ? Give some account of the arguments and experimental 
evidence which lead you to prefer your explanation to others that 
have been suggested. (Mech. Sc. Tripos, 1904.) 

17. Discuss the reasons that have been given for the so-called " sup- 
pression of heat " in the working mixture of a gas engine, and give an 
account of recent investigations, conducted for this purpose, into the 
properties of the gas used and into the interchange of heat between 
the mixture and the iron surface into which it comes in contact during 
its working. (Mech. Sc. Tripos, 1911.) 

18. Describe with sketches how lubrication of the various parts of 
an engine (not encased) is usually performed. (B. of E., 1902.) 

19. Why do we regulate an engine with both a flywheel and a gover- 
nor ? Explain clearly how each affects the regulation. 

(B. of E., 1900.) 

20. Give an account of the different methods used for governing 
gas engines, stating the advantages and the disadvantages of each. 

(Mech. Sc. Tripos, 1904.) 

21. Sketch a section through the gas valve of a gas engine, show- 
ing the hit-and-miss mechanism operated by the governor. 

(B. of E., 1907.) 

22. Describe any non-luminous gas-making plant for use with a 
gas engine working to, say, 100 I.H.P. What chemical action takes 
place in the gas manufacture ? What is the composition of the gas ? 

(B. of E., 1899.) 

23. Describe with sketches the manufacture of any kind of producer 
gas. You must show that you have a knowledge of the chemical 
changes which occur. (B. of E., 1911.) 

24. A petrol engine is run on the brake and the petrol supply is 
gradually increased by adjustment of the carburettor, the throttle 
being kept fully open and the brake adjusted so as to keep the speed 
constant. It is found that the brake load increases to a maximum 
and then keeps nearly constant, in spite of a considerable increase 
in the consumption of petrol. Also the maximum torque so deter- 
mined diminishes as the speed is increased. Explain these observa- 
tions. (Mech. Sc. Tripos, 1913.) 

25. Describe some form of small 2-cycle petrol motor. Explain 
why the small 2-cycle engines do not as a rule give much more power 
than the 4-cycle engines of equal cylinder capacity and are consider- 
ably less economical of fuel. What countervailing advantages have 






304 THE INTERNAL COMBUSTION ENGINE 



""-'- '- '..- -"" 7~*~ - :z :-■ zzlzz : . ;: -; zz-^r-r. _i :::_„- 



(2) When going at slow speed up a fain of 1 in 5. 

"".. " -= "..- _: .'.:■": -t .:-- >zzrJz .:.-;■ • :.- :•: v.- ::/::^:- '.;-.;: -_._ T r-": 
box and the back axle gear ? 

©f thes£rdbearegiiir@afay«»^14j- — | where <*•» is the angular Telocity of 

-'...- :■: .. " .. :- ". -^ - : : . i :-:zzzz.^:zzzzs: : 

pfeeh. 8c Tr 1913 

_^ ~iLr z:1:-^zz-2 ■ : - "..- :-- ""'.:- :: :~ : : : i_-;.;-,:-/.::- ^ :—-- ::' :ii 

-'...- _ - -. Hr "_- I_T ------ ".- T --!_ 7JL-B '. : I"-1Z_Z ~ " -.~ "~ 

r.f-i~ Z TJiT .: - ::•:> ~i= -..- ' _:'.-: :_...vj. lz. :t«: A. izii '.:.- :~rz 

:-,- : :zzt"t >;zzz.~ z~~ z~-r?r.rz — 

A B 

V©L of gas ft»ke*> per stroke ((eu_ ft.) ... 0-10 
Work done per stroke ((per cent, of heat supply) . _" 

ZE> 2.- z-"""-i. : : ; - :z-r _ ~~ :-.:-: '-;;_-- _- : "__ _-., : szxr-v .29 "- 

The : : ml usti hi : : the gas was complete in both eases. What is 
the ~ xrlanatian of CI) the greater percentage heat loss in B. and (2) 

_5 inf ~z'""t: _.;-:-■: . .-- 7f ~ .:.:_:_: ::r :_.- ~zz - :z ~ ... - 

iz : [ in e m : i n i, iff not, how do you account for the balance f 

(Heeh. Sc Tripos, 1913.) 
29. Show that the force required to accelerate the reciprocating 

niv.-r-r- :_ .' -.1- riizii-.-: 1= "-"t::_ :-.": ":: : ziz_ :-.7t-~~ 17 

" _ - : : - - — — :os . _ . 

v 

. . : M = : - - : : . . : " - 

- - ; — ■ j ^ 



-■ — ^ :._'. :■■ — T- ::_ :•■" :- :':::"_i_t-i ~ 'Off E.. 1912.) 

:' J::"" T -!.-- -^-:- :- :;. ; -"-.-.- r- ;: : ^ -_■_■_- --:■;■,- -;z - "":.-:- .-. ":-::-:": 
:--: a.ssizj; z'zzz ..... ±^:rr"_f -i-t 7 ^ .--::. :. .... : ^..: :■: 

Ekperbnents with hydrogen have shown a very sligjat rise of tem- 

~'-Z'~--~ "z~ _~ . :.:_:. . .'. },•:■:• izzzzz ~.\z ~ • t,~ 



chap, ix] PETROL ENGINE EFFICIENCY 305 

31. In a single-cylinder engine, at any point of the stroke, show 
how to find the turning moment on the crankshaft, if we have an 
Indicator Diagram and the sizes and weights of the parts of the engine 
and its speed. Take the shortness of the connecting rod into account. 

(B. of E., 1910.) 

32. Given the PV diagram of air altering in state, how do we find 

rfH 
a diagram showing at every instant -==, the rate of reception of heat ? 

If the expansion curve follows approximately PV" = constant, find 
dH (B. of E., 1909.) 

dV' 

33. Explain how you would proceed to find the temperature of the 
charge in the cylinder of a gas engine at a point in the stroke just after 
the closing of the admission valve. Having determined this tempera- 
ture, how would you use it to find the temperature at points during 
the expansion stroke ? State clearly the measurements you would 
make and the observations you would take to obtain the necessary 
data. 



ANSWERS TO EXAMPLES 

CHAPTER II 

Pages 38-43 

1. 1182° C. 2. 74-8 lb. per sq. inch by gauge. 

3. 1870° C. 4. 1502° C. 

5. 1598° C. ; 234 lb. per sq. inch. 

6. 18-7 lb. ; 3,517 cu. ft. 

7. {a) 58-8 lb. per sq. inch ; 70° C. 
(6) 104 lb. per sq. inch ; 333° C. 

8. 114 lb. per sq. inch. 9. 66-4 lb. per sq. inch ; 109-5° C 
10. 330° F. ; - 63° F. 11. 500° C. 12. 30° F. 

15. Work done in adiabatic compression = 65,400 ft. lb. 
Work done in isothermal compression = 64,800 ft. lb 
Work done by air in final process = 26,500 ft. lb. 
Heat given to air = 92,000 ft. lb. 

16. - 67*5° C. ; 37-5 cu. ft. 17. 406 C.H.U. 

18. 13-6° F. ; 21-85 in. of mercury. 

19. (1) 3,047 ft. lb. (2) 296 ft, lb. gained. 
(3) 394° F. ; -33 cu. ft. 

20. 6-65 cu. ft. ; 440° C. ; 71-5 lb. per sq. inch. 

21. 892° F. 22. 29 B.Th.U. 

23. 0-566. 24. 75 lb. per sq. inch. 

25. (i) -0793 lb. (ii) 174-2 lb. per sq. inch ; 1185° F. abs. 
(hi) 2523° F. (iv) 545 lb. per sq. inch. 

(v) 46 lb. per sq. inch ; 1878° F. abs. 
(vi) 49-4 per cent, (vii) 83-8 per cent. 

26. (i) 1103° F. ; 1615° F. 

(ii) On explosion 26,980 ft. lb. of Heat received. 
On expansion 11,190 ft. lb. received. 
On exhaust 25,690 ft. lb. rejected, 
(hi) 32-5 per cent. 
28. 1-79 : 1. 29. By compressor ; 20 H.P., 7-45d. per hour. 

By direct heating, l-Sd. per hour. 

CHAPTER III 

Pages 64-65 
1. 27 ft. lb. 

306 



ANSWERS TO EXAMPLES 307 

CHAPTER IV 

Pages 97-99 

1. 107 C.H.U. 2. (i) y = 1-37. (ii) 7-55 cu. ft. 

•00194 (1-37 — s) P C.H.U. per cu. ft. when the pressure is 
5,000 lb. per square foot. 

3. (i) 27° C. (ii) 177° C. (iii) 25-4 C.H.U. ; 62-4 C.H.U. received. 

4. 102-5 lb. per sq. inch ; work done, 144,000 ft. lb. ; 103 C.H.U. 

carried away. 



CHAPTER V 
Pages 165-169 

1. 6'7 H.P. 2. 20 H.P. 3. 94,700 ft. lb. 

4. 81 H.P. ; 68-3 H.P. ; 84-3 per cent. 

5. 666 H.P. ; 81-8 per cent. ; 91-9 cu. ft ; 112 cu. ft. ; 25-7 per 

cent. ; 21 per cent. 

6. 56-6 H.P. ; 45-5 H.P. ; 80-4 per cent. 

8. 45 H.P. ; 33-3 per cent. 9. 58-3 per cent. 

11. 1-3 tons. 12. 155° C. 

13. 2-58 x 10 5 ft.-lb. ; 2-65 x 10 4 ft.-lb. 

14. 7-96 ft. ; 48 tons. 16. 39-2 ; 9-9 tons wt. 
17. 466°C; 1:57: 1-67; 1-81 : 20 H.P. 



CHAPTER VI 
Pages 203-204 

1. 126,000; 41,300; 42,000; 42,700 C.H.U. 

2. 8,346 C.H.U. per lb. ; 11-56 lb. of air. 

3. 25-3 per cent. ; -46 per cent, lost in jacket-cooling water; 79*2 

per cent, lost in exhaust. 

4. 1,002 C.H.U. per hour indirect heating; 8,200 C.H.U. per hour 

direct heating ; 0*122. 



CHAPTER VII 

Page 216 

1. 35-4 per cent. 2. 666 H.P. ; 81-8 per cent. ; 91-9 cu. ft, ; 112 

cu. ft. ; 25-7 per cent. ; 21 per cent. 



308 ANSWERS TO EXAMPLES 

CHAPTER VIII 

Pages 274-276 

1. 14-75 per cent. 2.^ Excess air 106-6 per cent. ; exhaust products 
per lb. of oil. 32-1 lb. 

3. O, 96 grams ; C0 2 , 88 grams : H 2 0, 54 grams. 

4. Indicated thermal efficiency. 18-9 per cent. 

5. 11.360 C.H.U. per lb. ; 3-49 lb. of O. 

6. 1-07 in. ; 75 lb. per sq. inch ; 240 lb. -ft. ; 5-8 H.P. 

7. 8-8 H.P. 8. 210 lb.-ft. ; 3-57 ; 450 lbs. 
9. -655. 10. 20-5 per cent. ; 78-9 per cent. 

11. 67-6 lb. per sq. inch. 

12. -819^P ( _y_ \*/_2x 1 

V T \y -f / Vy+ 1/ 
where a sq. feet is the contracted area of the issuing jet. 



CHAPTER IX 

Page 301 

1. (i) 60; 72. (ii) 26; 38. (iii) 20; 22. (iv) 8: IS 

2. 105 ; 84 ; 70 lb. per sq. inch. 



INDEX 

References are to pages 



Absolute temperature, 15 

Acceleration and hill-climbing 
ability of motor cars, 298 
Accelerometer, 295, 296 
Adam M. Atkinson, tests on 

Dowson Gas Plant, 184 
Adiabatic curves, 19, 32-34, 82 
with variable specific heat, 82 
gas equations (const, sp. lit.), 20 

(var. sp. ht.), 75 
transformations, 20, 34, 74 
Aeronautical engines {see also 

Engines), 246-248 
After-burning theory, 47 
Air, heat contents of dry and 
saturated, 37 
composition and density of, xvi 
laws relating to expansion, 
pressure and temperature 
of, Chaps. II and IV 
needed for combustion, 229, 

288, 290 
ratio of specific heats of, 18 
resistance to motor cars, 245, 

297, 298 
specific heat at constant pres- 
sure, 12 
at constant volume, 12 
standard of efficiency, 36, 281 
Air pressure, effect on power of 

engines of, 124 
Alcohol, air required for com- 
bustion of, 224, 228 
calorific value of, 222, 223 
composition of, 222 
corrosive effect of, 224 
cost of production of, 225, 226 
flexibility of, as a fuel, 224, 229 



Alcohol, percentage of water in, 
224 
rapidity of combustion of, 223 
safety of, 222 

sources of production of, 225 
specific gravity of, 222 
thermal efficiency of, 223, 224 
use of benzol with, 224, 226 
use of high compression with, 

223 
volatility of, 222, 225 
Alexander and Bairstow, experi- 
ments on explosion pres- 
sures, 54 
Alternators, effect of cyclic irregu- 
larity on paralleling of, 156 
Altitude, decrease of engine 

power with, 124 
Aluminium, manufacture of, by 

surplus power, 213 
Ammonia from gas plants, re- 
covery of, 176, 188 
Analysis of exhaust gases, 291-293 
Andrews L. , on costs of steam and 

gas power plants, 189 
Anna colliery, surplus gas power 

at, 209 
Armengaud Rene, gas turbine of, 

117 
Atmospheric pressure on power of 

engines, effect of, 124 
Atomic weights, xvi 
Ayrton and Perry, on heat ex- 
change in cylinder con- 
tents, 70 

Back pressure of exhaust gases, 
287 



309 



310 



INDEX 



Bailly and Kraft, on use of blast- 
furnace gas in engines, 207 
Bairstow and Alexander, ex- 
plosion experiments of, 54 
Balancing of engines, 160-165 
Ballantyne, on analysis of Dow- 
son gas, 184 
Benzol, air required for combustion 
of, 228 
calorific value of. 221. 222 
composition of, 221, 222 
as a fuel, flexibility of. 229 
freezing of, 222 

specific gravity of, 221. 222. 226 
sulphur in. 226 

use of alcohol with. 224. 226 
volatility of. 221, 222 
Bessemer Works, gas cleaning 

plant at, 213 
Bibbins, J. R., on hydrogen 

contents of gases. 188 
Blount, Bertram, on analysis of 
anthracite, 184 
on power from surplus gas. 214 
Boyle's Law. 15 

Brake-horse-power, calculation of. 

138 (see also Horse -power) 

Brake-mean-pressure (v~P) in 

petrol engines, 279, 288 
Brayton engine, 35 
British Thermal Unit. 11. xv 
Burrows, Shober, tests on pres- 
sure-producer plant, 185 
Burst all, Prof., 47 

on engine efficiency by water 

injection, 121 
on temperatures in gas engines, 
75 
By-products of coke ovens, 209 
of producers, 176, 188 



Calcium carbide, use of surplus 
gas for manufacture of, 213 
Calcium cvanamide, 215 
Callendar." Prof., 35, 48 

experiments on measuring gas 

engine temperatures, 76 
formula for horse-power of 

petrol engines, 285 
on ideal engine dimensions, 281 
Calorie, heat unit, 11. xv 



Calorific value of alcohol. 222. 223 
of benzol. 221. 222 
of blast-furnace gas. 30. 205, 

208, 229 
of carbon, 170, 172 
of coal, 7, 44 

of coal gas, 30. 44. 188, 229 
of coke-oven gas. 30. 205. 208- 

210. 229 
of Diesel oil, 7 

of explosive mixtures, 188, 229 
of hydrogen, 171-174 
of oil vapours. 188. 229 
of paraffin. 221, 222. 256 
of petrol, 44. 221. 256. 278 
of petroleum, 7, 44 
of producer gas. 30. 145. 146. 
174-176. 185-188. 229 
Capitaine Herr, on cleaning of 

gases, 194 
Carbon deposit from paraffin. 254 
Carburettors, automatic. 252 
Claudel-Hobson, 252 
Cottrell paraffin. 254-255 
heating of air supply to. 228. 253 
jet. 247-257 
Krebs. 251 

Lanchester surface. 250 
theory of jet, 257-261 
Thorny croft paraffin. 256 
setting of, 294 
White and Poppe, 253 
Zenith, 252 
Cargo Fleet Iron Works, gas 

engines at, 112 
Carnofs Cycle, 27. 31 
Cecil. Rev. W.. earlv gas engine 

of, 2 
Centigrade scale of temperature. 1 5 
Charles' Law, 15 
Chemical formula of various gas - 
xvi 
manure, manufacture of. 215 
Clerk, Dugald. on explosion pres- 
sures. 47, 48. 54 
fuel efficiency tests of motor 

cars. 294 
on gas turbines. 118 
on heat losses in ^as engines. 

141-144 
on improving efficiency by 
super-compression, 120. 124 



INDEX 



311 



Clerk, Dugald, on rapidity of 

combustion, 55 
two -stroke cycle engine of, 4, 

106 
on volumetric heat of gaseous 
mixtures, 60, 79 
Coal, calorific value of, 7, 44 

world's output of, 220 
Coal engine, Dr. Low's, 196 
Cockerill Co., early experiments 
with blast -f urnace gas by, 
207 
gas engines of, 112 
Coke, annual output of, 208 
Coke ovens, 209 

by-products of, 209 
Coke oven gas, calorific value of, 
205, 209, 229 
composition of, 30, 205, 208, 
210 
Coker, Prof., on temperatures in 
gas engine cylinders, 78, 90 
Combustion, air needed for, 229, 
288, 290 
and explosion, Chap. Ill 
of petrol, conditions affecting, 

294 
rapidity of, 55, 58 
Commutators in ignition systems, 

265-267 
Compression, use of, 3, 4 

super-, for improving efficiency, 
120, 124 
Compression pressures in carbu- 
retted paraffin engines, 254 
in Diesel engines, 235, 236 
in gas engines, 37, 206, 113 
in oil engines, 236 
in semi-Diesel engines, 236 
Compression ratio, 4 

effect of alcohol on, 223 
effect of hydrogen on, 188, 207, 

209 
effect on efficiency of, 36 
in Diesel engines, 236 
in petrol engines, 277, 287- 
Condensers in ignition systems, 

265, 266 
Connecting rod, inertia of , 164, 165 
Constants, useful, xv, xvi 
Cooling by water injection, 120- 
123 



Cooling water, heat loss in, 140- 
144 
measurement of, 140, 145 
Cost of alcohol, 225, 226 

capital, for various types of 

engines, 7, 181, 189 
of fuel, etc., for various types of 

engines, 7, 190, 214 
of producer plants, 181, 182 
of water power, 214 
Coster, A. Vennell, on gas plant 

for marine use, 192 
Crankshaft, turning moment of, 

151 
Crosby indicator, 125 
Cycles, Carnot's, 27, 31, 35 

Clerk or two-stroke, 4, 103-106 

ideal standard, Chap. II 

Otto or four-stroke, 3, 35, 103, 

104 
Rankine, 31 
real working, 103, 104 
thermodynamic, Chap. II 
Cyclic irregularity, 155 

approximate method of com- 
puting, 159 
Cylinder cooling by water injec- 
tion, 120-123 
dimensions, effect on power and 

efficiency of, 280-283 
heat exchanges in contents of, 

68, 69, 72-74 
temperatures, 75-78, 89, 90 



Dalby, Prof., 160 

experiments on temperatures 

in gas engine, 76 
on fuel consumption of gas 
plant, 183 
Davey, Norman, on gas turbines, 

118 
Density of various gases, 18 

of air, xvi 
Diesel engine (see Engines) 
Dissociation of steam, latent heat 
of, 172 
theory, 46 
Donkin, Bryan, on pig-iron pro- 
duction, 206 
Douglas, experiments on ex- 
plosion pressures, 52 



312 



INDEX 



- ... 171 
on calorific values of produ: 
gas t 175 
. - nd-by losses :: -Trim and 
_ m B 1 v " 

Dust in blast -forna : - gases, 213 

Eeonc my : : van as _ s, 7 

Edge, S. J.. -:: " ■ . b tents n 

windage, 297, 298 
Rffi raan -Tandard sf, I 281 

rease ::. with increase :: 

=pf-:iz ? ^~ 

gas si mdard of, 78 8 
:: ideal standard cycles, Zmp. 

n 

:: ideal diagram :: Diesel en- 
gine 43 

mechanical, definition of. 14,139 
:: gas engines, 113. 121. _ '" 
of moGn ears, 245 
:: [ eta : I -i:ztt. _" x 
thermal, definition of. 22 
effect of cylinder dimensi : ns 

on. 280-28 
rz:: :: mZm [ 

.:. . " 
Hopkins m - m -mmm- on, 

86, K 
:: Z ieseJ t:.,o-- 7, 238 
::' gas engines, ~. 44. 113. 

121. 140-141 207 210 
improved bv water injection, 

119. 1Z 
iinproved jy sapex-compres- 

Bian, 120, 124 
of gas plants, 14-5. 18a 
:: Li~. plants, ma x imum . 171 
::' gas turbines. 117 
:: petrol engines -" v 285 

291 292 
:: steam engines, Z 44 
::' B&eam tarbines, ~. 119 
ZZZmrdt and Sehraer. 112 
Energy :: gasec intei o haps 

' ::: :-m:i iv 

unit of, xv 
Engines, capital costs :i wc also 
---" 7. 181, 18 
compression pressures in (see 

ressi :»n) 
efficienm- : 



Z nes, fuel consumption of (see 

Fuel C Misujnption 
heal losses in, 140-144 
history Z Internal Combustion, 

hap. I 
borse-f or of (see Hors e • 

■; ~m 
mechanical losses in. 131 
relation between Base and speed 
of. : 

- occupied bv various. 181. 
192 
testing of, 137-146 
teste :: see also Tests . 144- 

141 
weights : various (-5 Weight) 
aeronautical, 24Z- 248 

rburetted paraffin, Thomv- 
croft. 239-241 
: ?J. Dr. Low's, 1 
Diesel, Z 2Z:-_: 
doublo -acting, 1 104, 107- 

109, 112, 207 
gas. '. nap. V 
Bravton, 35 
: mmZeLZ 120, _" -232 
Rev. W. 

:ke:ml ! : s, 112 
\ 1 3 ssley, 145 
Fullagar, 110 
iriee, 1 " 
ZZmgZcm". 1 
Koerting, 107-109, 209 
Lenoir, 2 

Oechelhauser. 107. 110 
Otto, 3 

Otto and Ta d g on. 2 
Premier, 113 
Simplex. 2 " " 
Z; mrnyeroft, 194-196 
Tickers, 191 
hot bulb, 234, 2>" 
memm ZZ-Z-Z ,\ ':-.-.'. 
oil. Chap. VIE 
: mpbell, 2 
Hornsby, 234 
I mvcroft, 239-241 
Vickers. 191 
petrol. Chap. VILE 

lor maximum power of, 
_Z 

-:on of, 24 



INDEX 



313 



Engines, petrol, typical torque 
curve of, 279, 299 
Albion, 242 
Argyll, 248 
Arrol- Johnson, 110 
Austro-Daimler, 248 
Benz, 248 
Curtiss, 248 

Daimler, 5, 277-280, 291 
Day, 288 
De^Dion, 279 
Gobron-Brillee, 110 
Gnome, 246, 248 
Green, 248 
Mercedes, 248 
Regnault, 248 
Salmson, 248 
Sunbeam, 248 
Thorny croft, 239-241 
Vickers, 191 
Wolseley, 246-248 
reversible, 191, 238 
scavenging, 113 
semi-Diesel, 234, 235, 237 
two-stroke, 4, 103, 104, 106- 
112, 191, 238, 287, 28S 
Entropy, definition of, 22, 23 
unit of, 24 

examples in the use of, 25-34 
Eschweiler Mining Co. , surplus gas 

power plant of, 209 
Evaporation of liquid fuels, latent 
heat of, 227 
of water, latent heat of, 173, 227 
Exchanges of heat in cylinder 

contents, 68, 69, 72-74 
Expansion of gases, Chap. II 
Exhaust gases, back pressure of, 
287 
composition of, 290-294 
heat loss in, 140-144 
unburnt petrol in, 287, 289 
Explosion, time of, 55, 58 
pressures, 49, 52, 54 
temperatures, 57-60, 75, 89 
and combustion, Chap. Ill 



Fahrenheit scale of temperature, 

15 
Ferranti, on superheated steam 

turbines, 118 



Flashpoints of alcohol and petrol, 

223 
Flexibility of engines, effect of 
" pockets " on, 295 
of alcohol as a fuel, 224, 229 
of benzol as a fuel, 229 
of petrol as a fuel, 243 
Flow of heat through cylinder 

walls, 88, 90-97 
Flywheels, kinetic energy in, 154 
Mathot's formula for, 155 
steadying effect of, 154-160 
Friction losses in engines, 131, 139, 

141 
Fuel consumption of aeronautical 
engines, 247, 248 
of coal engine, 196 
of Diesel engine, 7, 238 
of gas and steam plants com- 
pared, 7, 186, 192 
of Humphrey pump, 117 
of marine gas plant, 196 
of marine steam plant, 196 
of oil engines, 192 
of petrol engines, 278, 280, 288, 

291 
of steam turbines, 7, 119 
tests on motor cars, 296, 300 
Fuels, calorific values of (see 
Calorific Values) 
costs of (see Costs) 
liquid, 219-229 
refining of liquid, 220 
Fuels Committee of Motor Union, 

Report of, 222 
Fullagar, H. F., engine of, 110 



Gas engines (see Engines) 
Gas plants, efficiency of (see 
Efficiency) 
fuel consumption of (see Fuel 

Consumption) 
for marine use, 190-196 
instructions for operating, 

196-203 
water consumption of, 145, 
172, 181-184, 188 
producers (see Producers) 
standard of efficiency, 78, 86 
power available from surplus 
(see Power) 



314 



IXPEX 



- turbines, 103. 117. 118 
washer. Theisen, 210 
Gaseous Explosions Committee 
investigations of. 62—64. 79 
Gases, blast-furnace and coke- 
oven. Chap. VII 
calorific values of various 

Calorific Values) 
chemical formula, for various, 

xvi 
combustion and explosion of. 

Chap. HE 
composition of various. 30, 
175.. 185, 195. 205, 208. 210 
density of various, 18 
internal energy of. Chap. IV 
laws relating to, Chaps. II and 

IV 
molecular weights of various, 

xvi 
quantity of dust in. 213 
volumetric heat of. 13. 60. 63 
specific heat of (see Specific 
Heat) 
Gasoline (see also Petrol). .. 
Governing. *' Hit and Miss."" 148 
exhaust. 149 
quantity. 150 
by retarding ignition. 150 
Governors, engine. 146-148 
Greiner, on power from surplus 

gas, 206 
Grover, experiments on explosion 
of gases, 50—54 



Harrison, J., on inertia of con- 
necting rod, 164 
H.A.S. tests on producer gas 

plants, 181 
Heat balance sheets, 140 

contents of saturated air, 37 
exchanges in cvlinder contents, 

407 Ex. 14; 68. 69. 72-74 
flow through cvlinder walls, 88 

90-97 
latent (see Latent Heat) 
loss to cvlinder walls, 68, 143, 

283 
loss in exhaust gases.. 140-144 
loss in water jacke* M -142 
losses in petrol engines, 281 



Heat, mechanical equiva^_ 
14, xv 

specific (see Specific Heat) unit 

of, XV, 11 

volumetric, 13, ©ft, 63 
High tension ignitioz. m Ijgpita on 
Hill -climbing tests of motor ears. 

. j 1 
History of internal combustion 

engines. Chap I 
Hoffmann, Dr. . : :. r : mailable 

from surpr_ - ^ - . 
Hogg, on heat exchan^ - _:_ rlin- 

dex contents. 72-14 
Holzwarth's gas turbine. 118 
Hopkinson, Pre : - x f : "_:_. t :." - :. 
gaseous explos. . :.- 
57 
on cylinder tempr : " j - - 
on cylinder cooling entirely 
by "water injection. 120-124 
onfrietion _ • - - m - ,.i.t- II 
on thermal t ~ . .. - :.. . - - 
engiines, 86 
tests on Dai ml er :>r ?:■:". ri^-i.- 

" 277-279. 291. 292 
reflecting ind; :.".-.: 1 2» 
Horse-power, brakr • :■; . . :. 
of, 138 
calculation of indicated-. 131, 

138 
Callendaris fornix^ 
definition of, 14 
effect of altitude and air pres- 
sure on. 131 
of carburetted paraffin engines, 

2M:. 2-55 
of motor ears, 395, 300 
of petrol engines, 24 3. 245, 

271 .' 
R.A.C. formula : i 283 
Hot bulb engines Engines 

Hubert. Prof. H.. on power from 

surplus gas. i 
Hut - patent coke ovens, 209 

H um phrey gas pump. 6, 1*93, 

113-117 
Hydrogen contents of var. 
gases. 188 
effect on comp:ession ratio of, 

18€ . " 209 
calorific value : : '.".-.'- 



INDEX 



315 



Ignition, dual. 271 

effect of " pockets " on, 295 
Eisemann system of, 263 
governing by retarding, 150 
high tension coil, 263-266, 272, 

27:} 
hot bulb, 234, 237, 262 
Lodge system of, 267, 268 
low tension, 241, 269 
magneto systems of, 263, 268- 

270 
regulation of, 241, 271-273 
rapidity of, 55, 58 
timing of, 271-273, 295 
too early (see Pre -ignition) 
tube, 233, 261, 262 
types of electric, 262, 263 
Dr. Watson's experiments on, 

272-274 
Topham & Tisdall's experiments 

on, 279-280 
Indicators, analysis of motion of, 

132-136 * 
Crosby, 125 
Hopkinson, 128 
lag of, due to inertia, 130 
reflecting, 127 
vibrations of, 130-136 
Indicator diagrams, calculation of 

mean effective pressure 

from, 130 
from Diesel engine, 236 
Dugald Clerk's zig-zag, 61 
effect of " Hit and miss " 

governing on, 149 
effect of turbulence on, 55 
from gaseous explosion ex- 
periments, 58 
from gas engines, 55, 72, 130 
from petrol engines, 274 
ideal (see Chap. II) 
showing suction, 150 
various, 29, 72 
Induction coils, 263-268 
Inertia of connecting rod, 164 
of flywheel, 154-160 
of reciprocating parts, 153, 

161-165 
Instructions for operating gas 

plants, 196-203 
Insulation resistance of sparking 

plugs, 280 



Iron, annual production of, 205, 
206 



Johannesburg generating station, 

112 
Joule's equivalent, 13, 14, 16, 19 
law of thermodynamics, 67 

Karovodine's gas turbine, 118 

Kerosene (see Paraffin) 

Kopper's regenerator ovens, 209 

Langen, experiments on gaseous 

explosions, 63 
Latent heat of dissociation of 
steam, 172 
of liquid fuels, 227 
of water, 173, 227 
Le Chatelier and Mallard, on 
variation of specific heat, 
46-48, 63 
Lewes, Vivian B., on sources of 

petrol supply, 227 
Lodge system of ignition, 267, 268 

sensitive trembler, 268 
Losses, heat, to cylinder walls, 68, 
143, 282 
in exhaust gases, 140-144 
in water jacket, 140-142 
in petrol engines, 281 
mechanical, in engines, 131, 139 

in motor cars, 245 
stand-by, of gas and steam 
plants, 187 
Low, Dr. A. M., coal engine of, 196 

Magneto, high tension, 270 

ignition (see Ignition) 
Mallard and Le Chatelier, on 

variation of specific heat, 

46-48, 63 
Manure, manufacture of chemical, 

214 
Marine propulsion, gas plants for, 

190-196 
Thornycroft oil engine for, 239- 

241 
Mathot on efficiency of large 

gas engines, 112, 113, 144, 

145 



316 



INDEX 



Mathot, formula for size of fly- 
wheels, 155 
McKechnie J., on internal com- 
bustion engines for war- 
ships, 191 
Mean-effective-pressure, calcula- 
tion of, 129, 130 
in petrol engines, 278, 279 
in two-stroke petrol engine, 288, 
289 
Mean-pressure in large gas engines, 
210 
in petrol engines, 278, 279 
in two-stroke petrol engine, 
288, 289 
Mechanical efficiency (see 

Efficiency) 
Mechanical equivalent of heat, 14, 

xv 
Milton, J. T., on gas plant for 

marine propulsion, 190 
Molecular weights of various gases, 

xvi 
Mond gas producer, 175 (see also 

Producers) 
Morse, L. G., experiments on 
composition of exhaust 
gases, 291 
Motor cars, air resistance of, 245, 
297, 298 
diagram of chassis, 243 
fuel efficiency of, 296, 300 
horse-power of, 295, 300 
mechanical efficiency of, 245 
RA.C. tests of, 300 
road testing of, 295-300 
Talbot, 244 

transmission losses in, 245 
weights of, 300 

tractive or road resistance of, 
295, 297 



Naphtha (see Benzol) 

wood, as a denaturant for 
alcohol, 227 
Nicholson, J. T., on efficiency of 
gas engines, 145 

Oils, calorific values of (see Calorific 
Value) 
crude, refining of, 220 



Oils, crude, density, output, 
sources of supply and com- 
position of, 220 
light (see Benzol and Petrol) 
lubricating, 221 

consumption of, 248, 256 
paraffin (see Paraffin) 
tar, 239 

Oil engines (see Engines) 
Ormandy, Dr. W. P., on alcohol 
as a substitute for petrol, 
224 
Otto cycle, 3, 35, 103, 104 



Paraffin, air required for combus- 
tion of, 228 
calorific value of, 221, 222, 256 
composition of, 221 
specific gravity of, 221, 222 
volatility of, 221, 222 
Paraffin carburettors (see Car- 
- buret tors) 
engines (see Engines) 
vaporizer, 232 
wax, 221 
Perry, Prof., 257 

on thermodynamics, 70 
on balancing of engines, 160 
Petrol, air required for combus- 
tion, 228, 288, 290 
annual consumption of, 221 
calorific value of, 221, 222, 256, 

278, 291 
composition of 221, 222, 228, 

290 
conditions affecting complete 

combustion of, 294 
flexibility of, as a fuel, 229 
sources of supply, 227 
specific gravity of, 221, 222, 291 
unburnt, in exhaust gases, 287, 

289 
volatility of, 220, 222 
Petrol consumption (see Fuel Con- 
sumption) 
P.C. (petrol-consumption) rating 

of horse power, 285 
Petrol engines (see Engines) 
Petroleum, crude (see Oils, crude) 
Pig-iron, annual production of, 
205-208 



INDEX 



317 



Piston, analysis of motion of 

162, 163 
inertia of, 164 
of petrol engine, 243 
" Pockets," effect of, on efficiency, 

flexibility and ignition, 295 
Power available from surplus 

gas, 206-209 
from surplus gas, cost of, 214 
effect of altitude and air pres- 
sure on engine, 124 
unit of, xv, 14 
utilization of surplus, 213 
water, cost of, 214 
horse (see Horse-power) 
Pre-ignition, effect of hvdrogen 

on, 188, 207, 209 
in carburetted paraffin engines, 

255 
in oil engines, 236 
Pressure, air, effect on engine 

power of, 124 
back, of exhaust gases, 287 
brake-mean (rj P), in petrol 

engines, 279, 288 
compression, in engines (see 

Compression Pressure) 
compression, value of, 37 
of gaseous explosions, 49, 52, 54 
mean (see Mean Pressure) 
mean-effective (see Mean-effec- 
tive -pressure) 
in induction pipe, 278 
Producer gas, calorific values of, 

30, 145, 146, 174-176, 185, 

186, 188, 229 
composition of , 30, 175, 185, 195 
Producer gas plant, costs and 

economy of various, 181, 

182 
Dowson, tests on, 184, 185 
H.A.S., tests on, 181 
R.A.S. tests on, 182 
Producers, gas, Chap. VI 
Campbell, 177 
instructions for operating, 196- 

203 
maximum possible efficiency of, 

171 
Mond, 175 
National, 179 
Poetter, 112 



Producers, gas, quantity of water 
used in, 145, 172, 175 
tests on, 145, 181-185 
theory of, 170-176 
Pump, The Humphrey Gas, 6, 103, 
113 

Radiation, heat loss in engines by, 
141 

" Rank ", the unit of Entropy, 24 

Rankine cycle, 31 

Rapidity of ignition, 55, 58 

Rating of horse -power, Calen- 
dar's formula for, 285 
R.A.C. formula for, 283 

Ratio of compression (see Com- 
pression Ratio) 
of specific heats, 18, 281 

Redwood, Sir Boverton, on 
sources of petrol supply, 
227 

Reflecting Indicators, 127 

Resistance, air, 245, 297, 298 
tractive or road, 295, 297 

Richardsons, Westgarth & Co., 
112, 210 

Road tests of motor cars, 295-301 

Rossi, on power from surplus gas, 
206 

Rotter, Max, on power from sur- 
plus gas, 206 

R.A.C. formula for horse-power, 
283 
tests on motor cars, 300 

R.A.S. tests on producer plants, 
182 



Sankey, Capt., 28 
Scavenging of gas engines, 113 
Schiiler L., on cyclic irregularity, 

155 
Scoble, on temperatures in cylin- 
ders, 78 
Scrubber, Gas, Campbell, 177, 178, 
201 
centrifugal, 194 
National, 179 

water consumption in, 183, 184 
Semi-Diesel engines (see Engines) 
Shelton Iron Works power plant, 
209 



318 



INDEX 



Space occupied by gas plants, 181, 
192 
by oil engines, 192 
by steam plant, 192 
Spark, effect of character of, on 
engine power, 272-274 
effect of character of, on petrol 
consumption, 279, 280 
Sparking plugs, high tension, 267 
insulation resistance of, 280 
low tension, 241, 269 
Specific heat, definition of, 11 
difference of, 16 
at constant pressure, 12 
at constant volume, 12 
of gaseous mixture, 63, 64 
of various gases, 12, 18 
of various substances, 12 
ratio of, 18, 281 
variable, 46, 63, 64, 70, 79 
Speed of engines, variation of, 

146, 155-160 
Steam turbines, high efficiency of 

modern, 118 
Strickland, Mr., 267 
Super-compression, increase of 

efficiency by, 120, 124 
Surplus gas, utilization of, Chap. 
VII 

Tar from producers, extraction of, 

187, 194 
Temperature, absolute, 15 

Centigrade and Fahrenheit 

scales of, 15 
in gas engines, 75, 89, 90 
in cylinder walls, 89, 90 
suction, 77, 78 
Test Report Form for gas and oil 

engines, 141 
Testing of engines, 137-146 
Tests, gas engine, 144-146, 207, 
210 
gas plant, 145, 181-185 
on marine gas plant, 196 
on marine steam plant, 196 
petrol engine, 277-280, 288, 

291, 293 
motor car, 295-301 
Theisen gas washer, 210 
Theorv of jet carburettors, 257- 
261 



Thermal efficiency (see Efficiency) 
Thermodynamic cycles, Chap. II 
Thermodynamics, Chap. IV 

Joule's law of, 67 
Thermometer valve, Callendar's, 

76 
Thompson, Prof. S. P., on power 
from surplus gas, 206 
on cost of water power, 214 
Thwaite, B.H., on utilization of 

blast-furnace gas, 206 
Time of combustion, 55, 58 
Timing of ignition, 271-273, 295 
Timing valve in gas engines, 262 
Topham and Tisdall, on effect of 
character of spark on petrol 
consumption, 279, 280 
Torque curves of petrol engines, 

279, 299 
Trembler coils, 263-267 

Lodge sensitive, 268 
Tube ignition, 233, 261, 262 
Turbines, gas, 103, 117 
steam, 118 

steam, capital and running 
costs of, 189, 190 
Turning moment on crankshafts, 
151 

Unit of Entropy, 24 

of heat, xv, 11 

of power, xv, 14 

of work, xv, 13 
Unwin, Prof., 35 
Useful Constants, xv, xvi 

Valves, Callendar's thermometer, 
76 
Diesel engine, 235, 238, 239 
extra air (see Carburettors) 
gas engine, 105, 108, 120, 148 
needle (see Carburettors) 
oil engine, 231, 232 
petrol engine, 240, 241, 249 
sleeve and rotary, 245 
timing, 262 

Vaporization of liquid fuels, latent 
heat of, 227 
of water, latent heat of, 173, 227 

Vaporizer, paraffin, 232 (see also 
Carburettors) 



INDEX 



319 



Vaporizer, Hornsby type of, 233 
Vaseline, 221 

Volumetric heat, 13, 60, 63 



Washer, Theisen gas, 210 

Water consumption, in gas plants, 

145, 172, 181-184, 188 
latent heat of dissociation of, 

172 
latent heat of vaporization of, 

173, 227 
Water injection, cylinder cooling 

by, 120-123 
Water power, cost of, 214 
Wath Main Colliery, coke ovens 

at, 209 
Watson, Dr., on effect of char- 
acter of spark on engine 

power, 272-274 



Watson & Fenning, tests on two- 
stroke petrol engine, 288 
Weight, atomic, of various ele- 
ments, xvi 
of aeronautical engines, 246-248 
of gas engines, 181, 192 
of motor cars, 300 
of oil engines, 192 
of steam engines, 192 
relation of engine power to, 287 
molecular, of various gases, xvi 
Wimperis accelerometer, 296 
Windage, Edge's experiments on, 

297 (see also Resistance) 
W T ollaston, T. R., on capital costs, 

6 
Work, unit of, 13, xv 

Zero of absolute temperature, xvi, 
15 



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d'Albe, E. E. F., Contemporary Chemistry i2mo, 

Alexander, J. H. Elementary Electrical Engineering nmo, 

Allan, W. Strength of Beams Under Transverse Loads. I Science Series 

No. 19.) i6mo, 050 

Theory of Arches. (Science Series No. n.) i6mo, 

Allen, H. Modern Power Gas Producer Practice and Applications, imio, *2 50 

Gas and Oil Engines 8vo, *4 50 

Anderson, F. A. Boiler Feed Water 8vo, *2 5J 

Anderson, Capt. G. L. Handbook for the Use of Electricians 8vo, 3 00 

Anderson, J. W. Prospector's Handbook i2mo, 1 50 

And£s, L. Vegetable Fats and Oils 8vo, *4 oo 

Animal Fats and Oils. Trans, by C. Salter 8vo, *4 od 

Drying Oils, Boiled Oil, and Solid and Liquid Driers Svo, *5 00 

Iron Corrosion, Anti-fouling and Anti-corrosive Paints. Trans, by 

C. Salter 8 vo, *4 00 

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H. Robson 8vo, *2 50 

Andes, L. Treatment of Paper for Special Purposes. Trans, by C. Salter. 

i2mo, *2 50 



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Andrews, E. S. Reinfoiced Concrete Construction nmo, 

Theory and Design of Structures 8vo, 

Further Problems in the Theon' and Design of Structures. .. .8vo, 

Andrews, E. S., and Hey wood, H. B. The Calculus for Engineers. 121110, 
Annual Reports on the Progress of Chemistry. Nine Volumes now ready. ' 

Vol. I. 1904, Vol. IX, 191 2 8vo, each, 2 00 

Argand, M. Imaginary Quantities. Translated from the French by 

A. S. Hardy. (Science Series No. 52.) i6mo, o 50 

Armstrong, R., and Idell, F. E. Chimneys for Furnaces and Steam Boilers. 

(Science Series No. 1.) i6mo, o 50 

Arnold, E. Armature Windings of Direct-Current Dynamos. Trans, by 

F. B. DeGress 8vo, *2 00 

Asch, W., and Asch, D. The Silicates in Chemistry and Commerce . 8vo, *6 00 
Ashe, S. W., and Keiley, J. D. Electric Railways. Theoretically and 

Practically Treated. Vol. I. Rolling Stock i2mo, *2 50 

Ashe, S. W. Electric Railways. Vol. II. Engineering Preliminaries and 

Direct Current Sub-Stations i2mo, *2 50 

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Ashley, R. H. Chemical Calculations (In Press.) 

Atkins, W. Common Battery Telephony Simplified i2mo, *i 25 

Atkinson, A. A. Electrical and Magnetic Calculations 8vo, *i 50 

Atkinson, J. J. Friction of Air in Mines. (Science Series No. 14.) . .i6mo, o 50 
Atkinson, J. J., and Williams, Jr., E. H. Gases Met with in Coal Mines. 

(Science beries No. 13.) i6mo, o 50 

Atkinson, P. The Elements of Electric Lighting nmo, 1 50 

The Elements of Dynamic Electricity and Magnetism i2mo, 2 00 

Power Transmitted by Electricity i2mo, 2 00 

Auchincloss, W. S. Link and Valve Motions Simplified 8vo, *i 50 

Austin, E. Single Phase Electric Railways 4to, *5 00 

Ayrton, H. The Electric Arc 8vo, *5 00 

Bacon, F. W. Treatise on the Richards Steam-Engine Indicator . .nmo, 1 00 

Bailes, G. M. Modern Mining Practice. Five Volumes 8vo, each, 3 50 

Bailey, R. D. The Brewers' Analyst 8vo, *5 co 

Baker, A. L. Quaternions 8vo, *i 25 

Thick-Lens Optics nmo, *i 50 

Baker, Benj. Pressure of Earthwork. (Science Series No. 56.)...i6mo, 

Baker, I. 0. Levelling. (Science Series No. 91.) i6mo, 50 

Baker, M. N. Potable Water. (Science Series No. 61.) i6mo, o 50 

Sewerage and Sewage Purification. (Science Series No. i8.)..i6mo, o 50 

Baker, T. T. Telegraphic Transmission of Photographs nmc, *i 25 

Bale, G. R. Modern Iron Foundry Practice. Two Volumes, nmo. 

Vol. I. Foundry Equipment, Materials Used *2 50 

Vol. II. Machine Moulding and Moulding Machines *i 50 

Bale, M. P. Pumps and Pumping nmo, 1 50 

Ball, J. W. Concrete Structures in Railways 8vo, *2 50 

Ball, R. S. Popular Guide to the Heavens 8vo, *4 50 

Natural Sources of Power. (Westminster Series.) . . 8vo, *2 00 

Ball ; W. V. Law Affecting Engineers 8vo, *3 50 

Bankson, Lloyd. Slide Valve Diagrams. (Science Series No. 108.) . i6mo, 50 



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Barba, J. Use of Steal for Constructive Purposes 12010, 1 00 

Barnaul, G. B= Development of the Incandescent Electric Lamp. . . . 8vo, *2 00 

Barker, A. F. Textiles and Their Manufacture. | Westminster Series.") 8vo, 2 00 

Barker, A. F., and Midgley, E. Analysis of Textile Fabrics 8vo, 3 00 

Barker, A. H. Graphic Methods of Engine Design i2mo, *i 50 

■ Heating and Ventilation 4to, *8 00 

Barnard, J. H. The Naval Militiaman's Guide i6mo, leather 1 00 

Barnard, Major J. G. Rotary Motion. (Science Series No. 90.) i6mo, o 50 

Barrus, G. H. Boiler Tests 8vo, '3 00 

Engine Tests 8vo, *4 co 

The above two purchased together *6 00 

Barwise, S. The Purification of Sewage nmo, 3 50 

Baterden, J. R. Timber. (Westminster Series.) 8?o, *2 00 

Bates, E. L., and Charlesworth, F. Practical Mathematics i2mo, 

Part I. Preliminary and Elementary Course *i 50 

Part II. Advanced Course . . *i 50 

■ Practical Mathematics nmo, *i 50 

■ Practical Geometry and Graphics nmo, *2 co 

Batey, J. The Science of Works Management 121110, *i 25 

Beadle, C. Chapters on Papermaking. Five Volumes 12010, each, *2 00 

Beaumont, R. Color in Woven Design 8vo, *6 00 

Finishing of Textile Fabrics 8vo, *4 co 

Beaumont, W. W. The Steam-Engine Indicator 8vo, 2 50 

Bechhold, H. Colloids in Biology and Medicine. Trans, by J. G. 

Bullowa (In Press.) 

Beckwith, A. Pottery 8vo, paper, o 60 

Bedell, F., and Pierce, C. A. Direct and Alternating Current Manual. 

8vo, *2 00 

Beech, F. Dyeing of Cotton Fabrics 8vo, *3 00 

Dyeing of Woolen Fabrics 8 vo, *3 50 

Begtrup, J. The Slide Valve 8vo, *2 O o 

Beggs, G. E. Stresses in Railway Girders and Bridges. . . . .(In Press.) 

Bender, C. E. Continuous Bridges. (Science Series No. 26.) i6mo, o 50 

Proportions of Pins used in Bridges. (Science Series No. 4.) 

i6mo, o 50 

Bengough, G. D. Brass. (Metallurgy Series.) (In Press.) 

Bennett, H. G. The Manufacture of Leather 8vo, *4 50 

___ Leather Trades (Outlines of Industrial Chemistry). 8vo. . (In Press.) 
Bernthsen, A. A Text - book of Organic Chemistry. Trans, by G. 

UfGowan i2mo, *2 50 

Berry, W. J. Differential Equations of the First Species. i2mo. (In Preparation.) 
Bersch, J. Manufacture of Mineral and Lake Pigments. Trans, by A. C. 

Wright 8™. *5 00 

Bertin, L. E. Marine Boilers. Trans, by L. S. Robertson 8vo, 5 00 

Beveridge, J. Papermaker's Pocket Book i2mo, *4 00 

Bmnie, Sir A. Rainfall Reservoirs and Water Supply 8vo, *3 00 

Binns, C. F. Ceramic Technology 8vo, *5 00 

Manual of Practical Potting 8vo, *7 50 

The Potter's Craft i2mo, *2 00 

Birchmore, W. H. Interpretation of Gas Analysis i2mo, *i 25 



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Blaine, R. G. The Calculus and Its Applications i2mo, *i 5o 

Blake, W. H. Brewers' Vade Mecum 8vo, *4 00 

Blasdale, W. C. Quantitative Chemical Analysis. .. .i2mo. (In Press.) 

Bligh, W. G. The Practical Design of Irrigation Works 8vo, *6 00 

Bloch, L. Science of Illumination. Trans, by W. C. Clinton 8\o, *2 50 

Blok, A. Illumination and Artificial Lighting i2mo, 1 25 

Bliicher, H. Modern Industrial Chemistry. Trans, by J. P. Millington. 

bvo, *7 50 

Blyth, A. W. Foods: Their Composition and Analysis 8vo, 7 50 

■ Poisons: Their Effects and Detection 8vo, 7 50 

Bockmann, F. Celluloid i2mo, *2 50 

Bodmer, G. R. Hydraulic Motors and Turbines 12010, 5 00 

Boileau, J. T. Traverse Tables 8vo, 5 00 

Bonney, G. E. The Electro-platers' Handbook i2mo, 1 20 

Booth, N. Guide to the Ring-spinning Frame i2mo, *i 25 

Booth, W. H. Water Softening and Treatment 8vo, *2 50 

Superheaters and Superheating and Their Control 8vo, *i 50 

Bottcher, A. Cranes: Their Construction, Mechanical Equipment and 

Working. Trans, by A. Tolhausen 4to, *io 00 

Bottler, M. Modern Bleaching Agents. Trans, by C. Salter. . . .121110, *2 50 

Bottone, S. R. Magnetos for Automobilists nmo, *i 00 

Boulton, S. B. Preservation of Timber. (Science Series No. 82.) . i6mo, o 50 

Bourcart, E. Insecticides, Fungicides and Weedkillers 8vo, *4 50 

Bourgougnon, A. Physical Problems. (Science Series No. 113.) . i6mo, 050 
Bourry, E. Treatise on Ceramic Industries. Trans, by A. B. Searle. 

8vo, *5 00 

Bow, R. H. A Treatise on Bracing 8vo, 1 50 

Bowie, A. J., Jr. A Practical Treatise on Hydraulic Mining 8vo, 5 00 

Bowker, W. R. Dynamo, Motor and Switchboard Circuits 8vo, *2 50 

Bowles, O. Tables of Common Rocks. (Science Series No. i25.).i6mo, o 50 

Bowser, E. A. Elementary Treatise on Analytic Geometry 12010, 1 75 

Elementary Treatise on the Differential and Integral Calculus . nmo, 2 25 

Elementary Treatise on Analytic Mechanics nmo, 3 00 

Elementary Treatise on Hydro-mechanics i2mo, 2 50 

— — A Treatise on Roofs and Bridges i2mo, *2 25 

Boycott, G. W. M. Compressed Air Work and Diving 8vo, *4.oo 

Bragg, E. M. Marine Engine Design nmo, *2 00 

Design of Marine Engines and Auxiliaries (In Press.) 

Brainard, F. R. The Sextant. (Science Series No. 101.) i6mo, 

Brassey's Naval Annual for 191 1 8vo, *6 00 

Brew, W. Three-Phase Transmission 8vo, *2 00 

Briggs, R., and Wolff, A. R. Steam-Heating. (Science Series No. 

67.) i6mo, o 50 

Bright, C. The Life Story of Sir Charles Tilson Bright 8vo, *4 50 

Brislee, T. J. Introduction to the Study of Fuel. (Outlines of Indus- 
trial Chemistry. ) 8vo, *3 00 

Broadfoot, S. K. Motors, Secondary Batteries. (Installation Manuals 

Series.) i2mo, *o 75 

Broughton, H. H. Electric Cranes and Hoists *g 00 

Brown, G. Healthy Foundations. (Science Series No. 80.) i6mo, o 50 



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Brown, H. Irrigation 8vo, *5 oo 

Brown, Wm. N. The Art of Enamelling on Metal i2mo, *i oo 

Handbook on Japanning and Enamelling i2mo, *i 50 

. House Decorating and Painting i2mo, *i 50 

History of Decorative Art i2mo, *i 25 

Brown, Wm. N. Dipping, Burnishing, Lacquering and Bronzing 

Brass Ware i2mo, *i 00 

Workshop Wrinkles 8vo, *i 00 

Browne, C. L. Fitting and Erecting of Engines. 8vo, *i 50 

Browne, R. E. Water Meters. (Science Series No. 81.) i6mo, o 50 

Bruce, E. M. Pure Food Tests i2mo, *i 25 

Bruhns, Dr. New Manual of Logarithms 8vo, cloth, 2 00 

half morocco, 2 50 
Brunner, R. Manufacture of Lubricants, Shoe Polishes and Leather 

Dressings. Trans, by C. Salter 8vo, *3 00 

Buel, R. H. Safety Valves. (Science Series No. 21.) i6mo, o 50 

Burns, D. Safety in Coal Mines i2mo, *i 00 

Burstall, F. W. Energy Diagram for Gas. With Text 8vo, 1 50 

Diagram. Sold separately *i 00 

Burt, W. A. Key to the Solar Compass i6mo, leather, 250 

Burton, F. G. Engineering Estimates and Cost Accounts i2mo, *i 50 

Buskett, E. W. Fire Assaying i2mo, *i 25 

B utler, H. J. Motor Bodies and Chassis 8vo, *2 50 

Byers, H. G., and Knight, H. G. Notes on Qualitative Analysis . . . .8vo, *i 50 

Cain, W. Brief Course in the Calculus i2mo, *i 75 

Elastic Arches. (Science Series No. 48.) i6mo, o 50 

• Maximum Stresses. (Science Series No. 38.) i6mo, o 5G 

Practical Designing Retaining of Walls. (Science Series No. 3.) 

i6mo, o 50 

— — Theory of Steel-concrete Arches and of Vaulted Structures. 

(Science Series No. 42.) i6mo, o 50 

— — Theory of Voussoir Arches. (Science Series No. 12.) i6mo, o 50 

Symbolic Algebra. (Science Series No. 73.) i6mo, o 50 

Campin, F. The Construction of Iron Roofs 8vo, 2 00 

Carpenter, F. D. Geographical Surveying. (Science Series No. 37.).i6mo, 

Carpenter, R. C, and Diederichs, H. Internal Combustion Engines.. 8vo, *5 00 

Carter, E. T. Motive Power and Gearing for Electrical Machinery . 8vo, *5 00 

Carter, H. A. Ramie (Rhea), China Grass 12210, *2 00 

Carter, H. R. Modern Flax, Hemp, and Jute Spinning : . 8vo, *3 00 

Cary, E. R. Solution of Railroad Problems with the Slide Rule. . i6mo, *i 00 

Cathcart, W. L. Machine Design. Part I. Fastenings 8vo, *3 00 

Cathcart, W. L., and Chaffee, J. I. Elements of Graphic Statics . . 8vo, *3 00 

Short Course in Graphics i2mo, 1 50 

Caven, R. M., and Lander, G. D. Systematic Inorganic Chemis:ry.i2mo, *2 00 

Chalkley, A. P. Diesel Engines 8vo, *3 00 

Chambers' Mathematical Tables . 8vo, 1 75 

Chambers, G. F. Astronomy i6mo, *i 50 

Charpentier, P. Timber 8vo, *6 00 






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Chatley, H. Principles and Designs of Aeroplanes. (Science Series 

No. 126) i6mo, 

How to Use Water Power nmo, 

Gyrostatic Balancing 8vo, 

Child, C. D. Electric Arc 8vo, 

Child, C. T. The How and Why of Electricity i2mo, 

Christian, M. Disinfection and Disinfectants. Trans, by Chas. 

Salter i2mo, 

Christie, W. W. Boiler-waters, Scale, Corrosion, Foaming 8vo, 

Chimney Design and Theory 8vo, 

Furnace Draft. (Science Series No. 123.) i6mo, 

Water : Its Purification and Use in the Industries 8vo, 

Church's Laboratory Guide. Rewritten by Edward Kinch 8vo, 

Clapperton, G. Practical Papermaking 8vo, 

Clark, A. G. Motor Car Engineering. 

Vol. I. Construction *3 00 

Vol. II. Design (In Press.) 

Clark, C. H. Marine Gas Engines i2mo, *i 50 

Clark, D. K. Fuel: Its Combustion and Economy i2mo, 1 50 

Clark, J. M. New System of Laying Out Railway Turnouts i2mo, 1 00 

Clarke, J. W., and Scott, W. Plumbing Practice. 

Vol. I. Lead Working and Plumbers' Materials 8vo, *4 00 

Vol. II. Sanitary Plumbing and Fittings (In Press.) 

Vol. III. Practical Lead Working on Roofs (In Press.) 

Clausen-Thue, W. ABC Telegraphic Code. Fourth Edition . . . 121110, *5 00 
Fifth Edition 8vo, *7 00 

The A 1 Telegraphic Code 8vo, *7 50 

Clerk, D., and Ideil, F. E. Theory of the Gas Engine. (Science Series 

No. 62.) i6mo, o 50 

Clevenger, S. R. Treatise on the Method of Government Surveying. 

i6mo, morocco, 

Clouth, F. Rubber, Gutta-Percha, and Balata 8vo, 

Cochran, J. Concrete and Reinforced Concrete Specifications 8vo, 

Treatise on Cement Specifications 8vo, 

Coffin, J. H. C. Navigation and Nautical Astronomy i2mo, 

Colburn, Z., and Thurston, R. H. Steam Boiler Explosions. (Science 

Series No. 2.) i6mo, 

Cole, R. S. Treatise on Photographic Optics i2mo, 

Coles-Finch, W. Water, Its Origin and Use 8vo, 

Collins, J. E. Useful Alloys and Memoranda for Goldsmiths, Jewelers. 

i6mo, 
Collis, A. G. High and Low Tension Swit:h-Gear Design 8vo, 

Switchgear. (Installation Manuals Series.) i2mo, 

Constantine, E. Marine Engineers, Their Qualifications and Duties. 8vo, 

Coombs, H. A. Gear Teeth. (Science Series No. 120.) i6mo, 

Cooper, W. R. Primary Batteries 8vo, 

" The Electrician " Primers 8vo, 

Part I 

Part H 

Part in *2 



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Copperthwaite, W. C. Tunnel Shields 4to, *9 oo 

Corey, H. T. Water Supply Engineering 8vo [In Press.) 

Corfield, W. H. Dwelling Houses. Science Series No. 50.) .... i6mo, o 50 

Water and Water-Supply. Science Series No. 17.) i6mo, o 50 

Cornwall, H. B. Manual of Blow-pipe Analysis 8vo, *2 50 

Courtney, C. F. Masonry Dams 8vo, 3 50 

Cowell, W. B. Pure Air, Ozone, and Water i2mo, *2 00 

Craig, T. Motion of a Solid in a Fuel. (Science Series No. 49. i6mo, o 50 

Wave and Vortex Motion. (Science Series No. 43.) i6mo, o 50 

Cramp, W. Continuous Current Machine Design 8vo, *2 50 

Creedy, F. Single Phase Commutator Motors 8vo, *2 oo 

Crocker, F. B. Electric Lighting. Two Volumes. 8vo. 

Vol. I. The Generating Plant 3 d ) 

Vol. II. Distributing Systems and Lamps 

Crocker, F. B., and Arendt, M. Electric Motors 8vo, *2 50 

Crocker, F. B., and Wheeler, S. S. The Management of Electrical Ma- 
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Cross, C. F., Bevan, E. J., and Sindall, R. W. Wood Pulp and Its Applica- 
tions. (Westminster Series.) 8vo, *2 

Crosskey, L. R. Elementary Perspective 8vo, 1 00 

Crosskey, L. R., and Thaw, J. Advanced Perspective 8vo, 1 5P 

Culley, J. L. Theory of Arches. 1 Science Series No. 87.) i6mo, o 50 

Dadourian, H. M. Analytical Mechanics nmo, *3 00 

Danby, A. Natural Rock Asphalts and Bitumens 8vo, *2 53 

Davenport, C. The Book. (Westminster Series.) 8vo, *2 00 

Davey, N. The Gas Turbine 8vo, *4 oo 

Davies, D. C. Metalliferous Minerals and Mining 8vo, 5 ; 

Earthy Minerals and Mining 8vo, 5 00 

Davies, E. H. Machinery for Metalliferous Mines 8vo, 8 00 

Davies, F. H. Electric Power and Traction 8vo, *2 co 

Foundations and Machinery Fixing. (Installation Manual Series.) 

i6mo, *i co 

Dawson, P. Electric Traction on Railways 8vo, *o cc 

Day, C. The Indicator and Its Diagrams i2mo, *2 00 

Deerr, N. Sugar and the Sugar Cane 8vo, *8 00 

Deite, C. Manual of Soapmaking. Trans, by S. T. King 4to, *g co 

DelaCoux, H. The Industrial Uses of Water. Trans, by A. Morris. 8vo, *4 50 

Del Mar, W. A. Electric Power Conductors 8vo, *2 00 

Denny, G. A. Deep-level Mines of the Rand 4to, *io 00 

— — Diamond Drilling for Gold *5 00 

De Roos, J. D. C. Linkages. (Science Series No. 47.) i6mo, o 50 

Derr, W. L. Block Signal Operation Oblong nmo, *i 50 

— — ■ Maintenance-of-Way Engineering (In Preparation.) 

Desaint, A. Three Hundred Shades and How to Mix Them 8vo, *io 00 

De Varona, A. Sewer Gases. (Science Series No. 55.) i6mo, 50 

Devey, R. G. Mill and Factory Wiring. (Installation Manuals Series.) 

i2mo, *i 00 

Dibdin, W. J. Public Lighting by Gas and Electricity 8vo, *8 00 

Purification of Sewage and Water 8vo, 6 50 



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I ichmann, Carl. Basic Open-Hearth Steel Process 121110, *3 50 

Dieterich, K. Analysis of Resins, Balsams, and Gum Resins 8vo, *3 00 

Dinger, Lieut. H. C. Care and Operation of Naval Machinery . . . i2mo, *2 00 
Dixon, D. B. Machinist's and Steam Engineer's Practical Calculator. 

i6mo, morocco, 1 25 
Doble, W. A. Power Plant Construction on the Pacific Coast (In Press.) 

Dommett, W. E. Motor Car Mechanism nmo, *i 2 5 

Dorr, B. F. The Surveyor's Guide and Pocket Table-book. 

i6mo, morocco, 

Down, P. B. Handy Copper Wire Table i6mo, 

Draper, C. H. Elementary Text-book of Light, Heat and Sound . . i2mo, 

Heat and the Principles of Thermo-dynamics i2mo, 

Dubbel, H. High Power Gag Engines 8vo, 

Duckwall, E. W. Canning and Preserving of Food Products 8vo, 

Dumesny, P., and Noyer, J. Wood Products, Distillates, and Extracts. 

8vo, 
Duncan, W. G., and Penman, D. The Electrical Equipment of Collieries. 

8vo, 
Dunstan, A. E., and Thole, F. B. T. Textbook of Practical Chemistry. 

i2mo, 
Duthie, A. L. Decorative Glass Processes. (Westminster Series.) . 8vo, 

Dwight, H. B. Transmission Line Formulas 8vo, 

Dyson, S. S. Practical Testing of Raw Materials 8vo, 

Dyson, S. S., and Clarkson, S. S. Chemical Works 8vo, 

Eccles, R. G., and Duckwall, E. W. Food Preservatives . . . . 8vo, paper, o 50 
Eck, J. Light, Radiation and Illumination. Trans, by Paul Hogner, 

8vo, 

Eddy, H. T. Maximum Stresses under Concentrated Loads 8vo, 

Edelman, P. Inventions and Patents i2mo. (In Press.) 

Edgcumbe, K. "Industrial Electrical Measuring Instruments 8vo, 

Edler, R. Switches and Switchgear. Trans, by Ph. Laubach. . .8vo, 

Eissler, M. The Metallurgy of Gold 8vo, 

The Hydrometallurgy of Copper 8vo, 

The Metallurgy of Silver 8vo, 

The Metallurgy of Argentiferous Lead 8vo, 

A Handbook on Modern Explosives 8vo, 

Ekin, T. C. Water Pipe and Sewage Discharge Diagrams folio, 

Eliot, C. W., and Storer, F. H. Compendious Manual of Qualitative 

Chemical Analysis i2mo, 

Ellis, C. Hydrogenation of Oils 8vo, 

Ellis, G. Modern Technical Drawing 8vo, 

Ennis, Wm. D. Linseed Oiland Other Seed Oils 8vo, 

Applied Thermodynamics 8vo, 

Flying Machines To-day nmo, 

Vapors for Heat Engines i2mo, 

Erfurt, J. Dyeing of Paper Pulp. Trans, by J. Hubner 8vo, 

Ermen, W. F. A. Materials Used in Sizing 8vo, 

Evans, C. A. Macadamized Roads (In Press.) 



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10 D. VAN NOSTRAXD CO.'S SHORT TITLE CATALOG 
Ewing, A. J. Magnetic Induction in Iron 8vo, *4 oc 



*. 



Fairie, J. Notes on Lead Ores i2mo, ~i oo 

Notes on Pottery Clays i2mo, *i 50 

Fairley, W., and Andre, Geo. J. Ventilation of Coal Mines. (Science 

Series No. 58.) i6mo, o 50 

Fair weather, W. C. Foreign and Colonial Patent Laws 8vo, *3 00 

Fanning, J. T. Hydraulic and Water-supply Engineering 8vo, *5 oa 

Fauth, P. The Moon in Modern Astronomy. Trans, by J. McCabe. 

8vo, *2 00 

Fay, I. W. The Coal-tar Colors r 8vo, *4 00 

Fernbach, R. L. Glue and Gelatine 8vo, *3 00 

Chemical Aspects of Silk Manufacture nmo, *i 00 

Fischer, E. The Preparation of Organic Compounds. Trans, by R. V. 

Stanford i2mo, *i 25 

Fish, J. C. L. Lettering of Working Drawings Oblong 8vo, 1 00 

Fisher, H. K. C, and Darby, W. C. Submarine Cable Testing . . . .8vo, *3 50 
Fleischmann, W. The Book of the Dairy. Trans, by C. M. Aikman. 

8vo, 4 00 
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Vol. I. The Induction of Electric Currents *5 oo' 

Vol. II. The Utilization of Induced Currents *5 00 

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Centenary of the Electrical Current 8vo, *o 50 . 

Electric Lamps and Electric Lighting 8vo, *3 00 

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A Handbook for the Electrical Laboratory and Testing Room. Two 

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Fleury, P. Preparation and Uses of White Zinc Paints 8vo, *2 50 

Fleury, H. The Calculus Without Limits or Infinitesimals. Trans, by 

C. O. Mailloux (fn Press.) 

Flynn, P. J. Flow of Water. (Science Series No. 84.) . i2mo, 05a 

Hydraulic Tables. (Science Series No. 66.) i6mo, o 50 

Foley, N. British and American Customary and Metric Measures . .folio, *3 03 

Forgie, J. Shield Tunneling 8vo. (In Press.) 

Foster, H. A. Electrical Engineers' Pocket-book. (Seventh Edition.) 

121110, leather, §00 

Engineering Valuation of Public Utilities and Factories 8vo, *3 oo 

Handbook of Electrical Cost Data 8vo (In Press.) 

Foster, Gen. J. G. Submarine Blasting in Boston (Mass.) Harbor 4to, 350 

Fowle, F. F. Overhead Transmission Line Crossings i2mo, *i 50 

The Solution of Alternating Current Problems 8vo (In Press.) 

Fox, W. G. Transition Curves. (Science Series No. no.) i6mo, o 50 

Fox, W., and Thomas, C. W. Practical Course in Mechanical Draw- 
ing . . i2mo, 1 25 

Foye, J. C. Chemical Problems. (Science Series No. 69.^ i6mo, o 50 

Handbook of Mineralogy. (Science Series No. 86.) i6mo, o 50 

Francis, J. B. Lowell Hydraulic Experiments 4to, 15 00 

Franzen, H. Exercises in Gas Analysis i2mo, *i 00 



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Freudemacher, P. W. Electrical Mining Installations. (Installation 

Manuals Series.) i2mo, *i oo 

Frith, J. Alternating Current Design 8vo, *2 oo 

Fritsch, J. Manufacture of Chemical Manures. Trans, by D. Grant. 

8vo, *4 oo 

Frye, A. I. Civil Engineers' Pocket-book i2mo, leather, *5 oo 

Fuller, G. W. Investigations into the Purification of the Ohio River. 

4to, *io oo 

Furnell, J. Paints, Colors, Oils, and Varnishes 8vo. *i oo 

Gairdne:, J. W. I. Earthwork 8vo {In Press.) 

Gant, L. W. Elements of Electric Traction 8vo, *2 50 

Garcia, A. J. R. V. Spanish-English Railway Terms 8vo, *4 50 

Garforth, W. E. Rules for Recovering Coal Mines after Explosions and 

Fires i2mo, leather, 1 50 

Gaudard, J. Foundations. (Science Series No. 34.) i6mo, 050 

Gear, H. B., and Williams, P. F. Electric Central Station Distribution 

Systems 8vo, *3 00 

Geerligs, H. C. P. Cane Sugar and Its Manufacture 8vo, *5 00 

— — World's Cane Sugar Industry 8vo, *5 00 

Geikie, J. Structural and Field Geology 8vo, *4 00 

- — Mountains. Their Growth, Origin and Decay 8vo, *4 00 

The Antiquity of Man in Europe 8vo, *3 00 

Georgi, F., and Schubert, A. Sheet Metal Working. Trans, by C. 

Salter 8vo, 3 00 

Gerber, N. Analysis of Milk, Condensed Milk, and Infants' Milk-Food. 8vo, 1 25 
Gerhard, W. P. Sanitation, Watersupply and Sewage Disposal of Country 

Houses i2mo, *2 00 

Gas Lighting (Science Series No. in.) i6mo, o 50 

Household Wastes. (Science Series No. 97.) i6mo, o 50 

House Drainage. (Science Series No. 63.) i6mo, o 50 

Gerhard, W. P- Sanitary Drainage of Buildings. (Science Series No. 93.) 

i6mo, o 50 

Gerhardi, C. W. H. Electricity Meters 8vo, *4 00 

Geschwind, L. Manufacture of Alum and Sulphates. Trans, by C. 

Salter 8vo, *5 00 

Gibbs, W. E. Lighting by Acetylene i2mo, *i 50 

Physics of Solids and Fluids. (Carnegie Technical School's Text- 
books.) *i 50 

Gibson, A. H. Hydraulics and Its Application 8vo, *5 00 

Water Hammer in Hydraulic Pipe Lines i2mo, *2 00 

Gilbreth, F. B. Motion Study 12010, *2 00 

Primer of Scientific Management 12010, *i 00 

Gillmore, Gen. Q. A. Limes, Hydraulic Cements an d Mortars 8vo, 4 00 

Roads, Streets, and Pavements i2mo, 2 00 

Golding, H. A. The Theta-Phi Diagram i2mo, *i 25 

Goldschmidt, R. Alternating Current Commutator Motor . .8vo, *3 00 

Goodchild, W. Precious Stones. (Westminster Series.) 8vo, *2 00 

Goodeve, T. M. Textbook on the Steam-engine i2mo, 2 00 

Gore, G. Electrolytic Separation of Metals 8vo, *3 50 



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Gould, E. S. Arithmetic of the Steam-engine i2mo, 

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High Masonry Dams. (Science Series No. 22.) i6mo, 

Practical Hydrostatics and Hydrostatic Formulas. (Science Series 

No. 117.) i6mo, 

Grataoap, L. P. A Popular Guide to Minerals 8vo, 

Gray, J. Electrical Influence Machines i2mo, 

— — Marine Boiler Design i2mo, 

Greenhill, G. Dynamics of Mechanical Flight 8vo, 

Greenwood, E. Classified Guide to Technical and Commercial Books. 8vo, 

Gregorius, R. Mineral Waxes. Trans, by C. Salter. i2mo, 

Griffiths, A. B. A Treatise on Manures . nmo, 

Dental Metallurgy 8vo, 

Gross, E. Hops 8vo, 

Grossman, J. Ammonia and Its Compounds i2mo, 

Groth, L. A. Welding and Cutting Metals by Gases or Electricity. 
I Westminster Series) 8vo, 

Grover, F. Modern Gas and Oil Engines 8vo, 

Gruner, A. Power-loom Weaving 8vo, 

Giildner, Hugo. Internal Combustion Engines. Trans, by H. Diederichs. 

4to, 

Gunther, C. 0. Integration 12010, 

Gurden, R. L. Traversa Tables folio, half morocco, 

Guy, A, E. Experiments on the Flexure of Beams 8vo, 

Haeder, H. Handbook on the Steam-engine. Trans, by H. H. P. 

Powles i2mo, 

Hainbach, R. Pottery Decoration. Trans, by C. Salter i2mo, 

Haenig, A. Emery and Emery Industry 8vo, 

Hale, W. J. Calculations of General Chemistry nmo, 

Hall, C. H. Chemistry of Paints and Paint Vehicles nmo, 

Hall, G. L. Elementary Theory of Alternate Current Working. .. .8vo, 

Hall, R. H. Governors and Governing Mechanism i2mo, 

Hall, W. S. Elements of the Differential and Integral Calculus 8vo, 

Descriptive Geometry 8vo volume and a 4to atlas, 

Haller, G. F., and Cunningham, E. T. The Tesla Coil nmo, 

Halsey, F. A. Slide Valve Gears nmo, 

The Use of the Slide Rule. (Science Series No. 114.) i6mo, 

Worm and Spiral Gearing. (Science Series No. 116.) i6mo, 

Hamilton, W. G. Useful Information for Railway Men i6mo, 

Hammer, W. J. Radium and Other Radio-active Substances 8vo, 

Hancock, H. Textbook of Mechanics and Hydrostatics 8vo, 

Hancock, W. C. Refractory Materials. (Metallurgy Series.) (In Press.) 

Hardy, E. Elementary Principles of Graphic Statics nmo, *i 50 

Harris, S. M. Practical Topographical Surveying (In Press.) 

Harrison, W. B. The Mechanics' Tool-book nmo, 1 50 

Hart, J. W. External Plumbing Work 8vo, *3 00 

Hints to Plumbers on Joint Wiping 8vo, *3 00 

Principles of Hot Water Supply 8vo *3 00 

Sanitary Plumbing and Drainage 8vo, *3 00 



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D. VAN NOSTRAND CO.'S SHORT TITLE CATALOG 13 

Haskins, C. H. The Galvanometer and Its Uses i6mo, 1 50 

Hatt, J. A. H. The Colorist square i2mo, *i 50 

Hausbrand, E. Drying by Means of Air and Steam. Trans, by A. C. 

Wright i2mo, *2 00 

Evaporating, Condensing and Cooling Apparatus. Trans, by A. C. 

Wright 8vo, *5 00 

Hausner, A. Manufacture of Preserved Foods and Sweetmeats. Trans. 

by A. Morris and H. Robson 8vo, 

Hawke, W. H. Premier Cipher Telegraphic Code 4to, 

■ 100,000 Words Supplement to the Premier Code 4to, 

Hawkesworth, J. Graphical Handbook for Reinforced Concrete Design. 

4to, 

Hay, A. Alternating Currents 8vo, 

Electrical Distributing Networks and Distributing Lines 8vo, 

Continuous Current Engineering 8vo, 

Hayes, H. V. Public Utilities, Their Cost New and Depreciation. . .8vo, 

Heap, Major D. P. Electrical Appliances 8vo, 

Heather, H. J. S. Electrical Engineering 8vo, 

Heaviside, O. Electromagnetic Theory, Vols. I and II. . . .8vo, each, 

Vol. Ill 8vo, 

Heck, R. C. H. The Steam Engine and Turbine 8vo, 

Steam-Engine and Other Steam Motors. Two Volumes. 

Vol. I. Thermodynamics and the Mechanics 8vo, 

Vol. II. Form, Construction, and Working 8vo, 

Notes on Elementary Kinematics 8vo, boards, 

Graphics of Machine Forces 8vo, boards, 

Hedges, K. Modern Lightning Conductors 8vo, 

Heermann, P. Dyers' Materials. Trans, by A. C. Wright 12 mo, 

Hellot, Macquer and D'Apligny. Art of Dyeing Wool, Silk and Cotton. Svo, 

Henrici, 0. Skeleton Structures Svo, 

Hering, D. W. Essentials of Physics for College Students 8vo, *i 75 

Hering-Shaw, A. Domestic Sanitation and Plumbing. Two Vols.. .8vo, *5 00 

Hering-Shaw, A. Elementary Science 8vo, *2 00 

Herrmann, G. The Graphical Statics of Mechanism. Trans, by A. P. 

Smith i2mo, 

Herzfeld, J. Testing of Yarns and Textile Fabrics 8vo, 

Hildebrandt, A. Airships, Past and Present 8vo, 

Hildenbrand, B. W. Cable-Making. (Science Series No. 32.) . . . .i6mo, 

Hilditch, T. P. A Concise History of Chemistry 12:110, 

Hill, J. W. The Purification of Public Water Supplies. New Edition. 

{In Press.) 

Interpretation of Water Analysis (In Press.) 

Hill, M. J. M. The Theory of Proportion Svo, 

Hiroi, I. Plate Girder Construction. (Science Series No. 95.). . .i6mo, 
Statically -Indeterminate Stresses i2mo, 

Hirshfeld, C. F. Engineering Thermodynamics. (Science Series No. 45.) 

i6mo, 

Hobart, H. M. Heavy Electrical Engineering Svo, 

Design of Static Transformers i2mo, 

Electricity .... Svo, 

Electric Trains -8vo, 



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50 


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I 4 D. VAN XOSTRAXD CO.'S SHORT TITLE CATALOG 

Hobart, H. M. Electric Propulsion of Ships 8vo, 

Hobart, J. F. Hard Soldering, Soft Soldering and Brazing i2mo, 

Hobbs, W. R. P. The Arithmetic of Electrical Measurements i2mo, 

Hofi, J. N. Paint and Varnish Facts and Formulas i2mo, 

Hole, W. The Distribution of Gas 8vo, 

Holley, A. L. Railway Practice folio, 

Holmes, A. B. The Electric Light Popularly Explained. ..i2mo, paper, 

Hopkins, N. M. Experimental Electrochemistry 8vo, 

Model Engines and Small Boats i2mo, 

Hopkinson, J., Shoolbred, J. N., and Day, R. E. Dynamic Electricity. 

(Science Series No. 71.) i6mo, 

Horner, J. Metal Turning 122:0, 

Practical Ironf ounding 8vo, 

Plating and Boiler Making 8vo, 

Gear Cutting, in Theory and Practice 8vo, 

Houghton, C. E. The Elements of Mechanics of Materials i2mc, 

Houllevigue, L. The Evolution of the Sciences 8vo, 

Houstoun, R. A. Studies in Light Production 121110, 

Hovenden, F. Practical Mathematics for Young Engineers i2mo, 

Howe, G. Mathematics for the Practical Man i2mo, 

Howorth, J. Repairing and Riveting Glass, China and Earthenware. 

8vo, paper, 

Hubbard, E. The Utilization of Wood-waste 8vo, 

Hiibner, J. Bleaching and Dyeing of Vegetable and Fibrous Materials. 

(Outlines of Industrial Chemistry.) 8vo, 

Hudson, 0. F. Iron and Steel. (Outlines of Industrial Chemistry.). 8 vo, 

Kumper, W. Calculation of Strains in Girders 12210, 

Humphrey, J. C. W. Metallography of Strain. (Metallurgy Series.) 

(In Press.) 
Humphreys, A. C. The Business Features of Engineering Practice.. Svo, *i 25 

Hunter, A. Bridge Work Svo. (In Press.) 

Hurst, G. E. Handbook of the Theory of Color 8vo, 

Dictionary of Chemicals and Raw Products 8vo, 

■ Lubricating Oils, Fats and Greases 8vo, 

Soaps 8vo, 

Hurst, G. H., and Simmons, W. H. Textile Soaps and Oils 8vo, 

Hurst, H. E., and Lattey, R. T. Text-book of Physics 8vo, 

Also published in three parts. 

Part I. Dynamics and Heat 

Part II. Sound and Light 

Part III. Magnetism and Electricity 

Hutchinson, R. W., Jr. Long Distance Electric Power Transmission. 

12210, 

Hutchinson, R. W., Jr., and Thomas, W. A. Electricity in Mining. 12210, 

(In Press.) 

Hutchinson, W. B. Patents and How to Make Money Out of Them. 

i2mo, 1 25 

Hutton, W. S. Steam-boiler Construction 8vo, 6 00 

Practical Engineer's Handbook 8vo, 7 00 

The Works' Manager's Handbook 8vo, 6 00 



-2 


00 


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Hyde, E. W. Skew Arches. (Science Series No. 15.) i6mo, 

Eyde, F. S. Solvents, Oils, Gums, Waxes 8vo, 

Induction Coils. (Science S3ri23 No. 53.) i6mo, 

Ingham, A. E. Gearing. A practical treatise 8vo, 

Ingle, H. Manual of Agricultural Chemistry 8vo, 

Inness, C. H. Problems in Machine Design i2mo, 

Air Compressors and Blowing Engines nmo, 

Centrifugal Pumps i2mo, 

The Fan nmo, 

Isherwood, B. F. Engineering Precedents for Steam Machinery . . .8vo, 
Ivatts, E. B. Railway Management at Stations 8vo, 

Jacob, A., and Gould, E. S. On the Designing and Construction of 

Storage Reservoirs. (Science Series No. 6) i6mo, 05c 

Jannettaz, E. Guide to the Determination of Rocks. Trans, by G. W. 

Plympton nmo, 1 50 

Jehl, F. Manufacture of Carbons 8vo, *.\ 00 

Jennings, A. S. Comm ercial Paints and Painting. (Westminster Series. ) 

8vo, *2 00 

Jennison, F. H. The Manufacture of Lake Pigments 8vo, *3 00 

Jepson, G. Cams and the Principles of their Construction 8vo, *i 50 

Mechanical Drawing 8vo (In Preparation.) 

Jockin, W. Arithmetic of the Gold and Silversmith nmo, *i 00 

Johnson, J. H. Arc Lamps and Accessory Apparatus. (Installation 

Manuals Series.) nmo, *o 75 

Johnson, T. M. Ship Wiring and Fitting. (Installation Manuals Series.) 

nmo, 
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Johnson, W. McA. The Metallurgy of Nickel (In Preparation.) 

Johnston, J. F. W., and Cameron, C. Elements of Agricultural Chemistry 

and Geology nmo, 

Joly, J. Radioactivity and Geology nmo, 

Jones, H. C. Electrical Nature of Matter and Radioactivity nmo, 

New Era in Chemistry nmo, 

Jones, M. W. Testing Raw Materials Used in Paint nmo, 

Jones, L., and Scard, F. I. Manufacture of Cane Sugar 8vo, 

Jordan, L. C. Practical Railway Spiral nmo, leather, 

Joynson, F. H. Designing and Construction of Machine Gearing . . 8vo, 
Jiiptner, H. F. V. Siderology : The Science of Iron 8vo, 

Kansas City Bridge 4to, 

Kapp, G. Alternate Current Machinery. (Science Series No. 96.). i6mo, 

Keim, A. W. Prevention of Dampness in Buildings 8vo, 

Keller, S. S. Mathematics for Engineering Students. 1 2mo, half leather. 

Algebra and Trigonometry, with a Chapter on Vectors *i 75 

Special Algebra Edition *i . 00 

Plane and Solid Geometry *i .25 

Analytical Geometry and Calculus *2 00 

Kelsey, W. R. Continuous-current Dynamos and Motors 8vo, *2 50 

Kemble, W. T., and Underhill, C. R. The Periodic Law and the Hydrogen 

Spectrum 8vo, paper, *o 50 



*0 


75 


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CO 


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60 


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00 





50 


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16 D. VAN NOSTRAND CO.'S SHORT TITLE CATALOG 

Kemp, J. F. Handbook of Rocks 8vo, . *i 50 

Kendall, E. Twelve Figure Cipher Code 4to, *i2 50 

Kennedy, A. B. W., and Thurston, R. H. Kinematics of Machinery. 

(Science Series No. 54.) i6mo, o 50 

Kennedy, A. B. W., Unwin, W. C, and Idell, F. E. Compressed Air. 

(Science Series No. 106.) i6mo, o 50 

Kennedy, R. Modern Engines and Power Generators. Six Volumes. 4to, 15 00 

Single Volumes each, 3 00 

Electrical Installations. Five Volumes 4to, 15 00 

Single Volumes each, 3 50 

Flying Machines; Practice and Design i2mo, *2 00 

Principles of Aeroplane Construction 8vo, *i 50 

Kennelly, A. E. Electro-dynamic Machinery 8vo, 1 50 

Kent, W. Strength of Materials. (Science Series No. 41.) i6mo, o 50 

Kershaw, J. B. C. Fuel, Water and Gas Analysis 8vo, *2 50 

Electrometallurgy. (Westminster Series.) 8vo, *2 00 

The Electric Furnace in Iron and Steel Production i2mo, *i 50 

Electro-Thermal Methods of Iron and Steel Production. .. .8vo, *3 00 

Kinzbrunner, C. Alternate Current Windings 8vo, *i 50 

Continuous Current Armatures 8vo, *i 50 

Testing of Alternating Current Machines 8vo, *2 00 

Kirkaldy, W. G. David Kirkaldy's System of Mechanical Testing. .4to, 10 00 

Kirkbride, J. Engraving for Illustration 8vo, *i 50 

Kirkwood, J. P. Filtration of River Wat2T3 4to, 7 50 

Kirschke, A. Gas and Oil Engines i2mo, *i 25 

Klein, J. F. Design of a High-speed Steam-en^in? 8vo, *5 00 

Physical Significance of Entropy 8vo, *i 50 

Kleinhans, F. B. Boiler Construction 8vo, 3 00 

Knight, R.-Adm. A. M. Modern Seamanship 8vo, *7 50 

Half morocco *9 00 

Knox, J. Physico-Chemical Calculations nmo, *i 00 

Fixation of Atmospheric Nitrogen. (Chemical Monographs, 

No. 4.) i2mo, *o 75 

Knox, W. F. Logarithm Tables (In Preparation.) 

Knott, C. G., and Mackay, J. S. Practical Mathematics 8vo, 2 00 

Koester, F. Steam-Electric Power Plants 4to, *5 00 

Hydroelectric Developments and Engineering 4to, *5 00 

Roller, T. The Utilization of Waste Products 8vo, *3 50 

■ Cosmetics 8vo, *2 50 

Kremann, R. Application of the Physico-Chemical Theory to Tech- 
nical Processes and Manufacturing Methods. Trans, by H. 

E. Potts 8vo, *2 50 

Kretchmar, K. Yarn and Warp Sizing 8vo, *4 00 

Lallier, E. V. Elementary Manual cf the Steam Engine 121210, *2 00 

Lambert, T. Lead and Its Compounds 8vo, *3 50 

Bone Products and Manures 8vo, *3 00 

Lamborn, L. L. Cottonseed Products 8vo, *3 00 

Modern Soaps, Candles, and Glycerin 8vo, *7 50 

Lamprecht, R. Recovery Work After Pit Fires. Trans, by C. Salter . 8vo, *4 00 

Lancaster, M. Electric Heating, Cooking and Cleaning 8vo, *i 50 



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Lanchester, F. W. Aerial Flight. Two Volumes. 8vo. 

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Lamer, E. T. Principles of Alternating Currents nmo. *i 25 

Larrabee, C. S. Cipher and Secret Letter and Telegraphic Code. i6mo, o 60 

La Rue, B. F. Swing Bridges. (Science Series No. 107.) i6mo, o 50 

Lassar-Cohn. Dr. Modern Scientific Chemistry. Trans, by M. M. 

Pattison Muir i2mo, *2 00 

Latimer, L. H., Field, C. J., and Howell, J. W. Incandescent Electric 

Lighting. (Science Series No. 57.) i6mo, o 50 

Latta, M. N. Handbook of American Gas-Engineering Practice . . . 8vo, *4 50 

American Producer Gas Practice 4to, *6 00 

Laws, B. C. * Stability and Equilibrium of Floating Bodies 8vo, *3 50 

Lawson, W. R. British Railways. A Financial and Commercial 

Survey 8vo, 200 

Leask, A. R. Breakdowns at Sea . nmo, 2 00 

— — Refrigerating Machinery i2mo, 2 00 

Lecky, S. T. S. " Wrinkles " in Practical Navigation 8vo, *8 00 

Le Doux, M. Ice-Making Machines. (Science Series No. 46.) . . i6mo, o 50 

Leeds, C. C. Mechanical Drawing for Trade Schools oblong 4to, 

High School Edition *i 25 

Machinery Trades Edition *2 . 00 

Lefevre, L. Architectural Pottery. Trans, by H. K. Bird and W. M. 

Binns 4to, *7 50 

Lehner, S. Ink Manufacture. Trans, by A. Morris and H. Robson . 8vo, *2 50 

Lemstrom, S. Electricity in Agriculture and Horticulture 8vo, *i 50 

Letts, E. A. Fundamental Problems in Chemistry 8vo, :|: 2 00 

Le Van, W. B. Steam-Engine Indicator. (Science Series No. 78.)i6mo, o 50 

Lewes, V. B. Liquid and Gaseous Fuels. (Westminster Series.) . .8vo, *2 00 

Carbonization of Coal 8vo, *3 00 

Lewis, L. P. Railway Signal Engineering 8vo, *3 50 

Lieber, B. F. Lieber's Standard Telegraphic Code 8vo, *io 00 

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Spanish Edition 8vo, *io 00 

French Edition 8vo, *io 00 

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Bankers and Stockbrokers' Code and Merchant and Shippers' 

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100,000,000 Combination Code 8vo, *io 00 

Engineering Code 8vo, *i2 50 

Livermore, V. P., and Williams, J. How to Become a Competent Motor- 
man i2mo, *i 00 

Liversedge, A. J. Commercial Engineering 8vo, *3 00 

Livingstone, R. Design and Construction of Commutators 8vo, *2 25 

Mechanical Design and Construction of Generators 8vo, *3 50 

Lobben, P. Machinists' and Draftsmen's Handbook 8vo, 2 50 

Lockwood, T. D. Electricity, Magnetism, and Electro-telegraph ... 8vo, 2 50 



18 D. VAN NOSTRAND CO.'S SHORT TITLE CATALOG 

Lockwood, T. D. Electrical Measurement and the Galvanometer. 

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Lodge, O. J. Elementary Mechanics i2mo, i 50 

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Vol. II. Varnish Materials and Oil Varnish Making *4 00 

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McMechen, F. L. Tests for Ores, Minerals and Metals i2mo, *i 00 

McPherson, J. A. Water-works Distribution 8vo, 2 50 

Melick, C. W. Dairy Laboratory Guide nmo, *i 25 

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H. E. Schenck 8vo, 1 00 

Merivale, J. H. Notes and Formulae for Mining Students 121110, 1 50 

Merritt, Wm. H. Field Testing for Gold and Silver i6mo, leather, 1 50 

Messer, W. A. Railway Permanent Way 8vo (In Press.) 

Meyer, J. G. A., and Pecker, C. G. Mechanical Drawing and Machine 

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Michell, S. Mine Drainage 8vo, 10 00 

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Milroy, M. E. W. Home Lace-making i2mo, *i 00 

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Mitchell, C. A. Mineral and Aerated Waters 8vo, *3 00 



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Elementary Course *i 50 

Advanced Course "2 50 

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Monteverde, R. D. Vest Pocket Glossary of English- Spanish, Spanish- 
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Morgan, A. P. Wireless Telegraph Apparatus for Amateurs i2mo, *i 50 

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Mullin, J. P. Modern Moulding and Pattern-making i2mo, 2 50 

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Nicol, G. Ship Construction and Calculations 8vo, *4 50 

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Nisbet, H. Grammar of Textile Design Svo. "3 00 

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Nugent, E. Treatise on Optics i2mo, 1 50 

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• Petrol Air Gas "mo, *o 75 



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Olsen, J. C. Text-book of Quantitative Chemical Analysis 8vo, *4 00 

Olsson, A. Motor Control, in Turret Turning and Gun Elevating. (U. S. 

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Ormsby, M. T. M. Surveying i2mo, 1 50 

Oudin, M. A. Standard Polyphase Apparatus and Systems 8vo, *3 00 

Cwen, D. Recent Physical Research 8vo, *i 50 

Pakes, W. C. C, and Nankivell, A. T. The Science of Hygiene . .8vo, *i 75 

Palaz, A. Industrial Photometry. Trans, by G. W. Patterson, Jr .. 8vo, *4 00 

Pamely, C. Colliery Manager's Handbook 8vo, *io 00 

Parker, P. A. M. The Control of Water 8vo, :; 5 00 

Parr, G. D. A. Electrical Engineering Measuring Instruments. .. .8vo, *3 50 

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I 


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75 


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D. VAN NOSTRAND CO.'S SHORT TITLE CATALOG 23 



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Rafter, G. W., and Baker, M. N. Sewage Disposal in the United States. 

4to, 

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Randau, P. Enamels and Enamelling 8vo, 

Rankine, W. J. M. Applied Mechanics 8vo, 

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8vo, 

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Rathbone, R. L. B. Simple Jewellery 8vo, 

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Redwood, B. Petroleum. (Science Series No. 92.) i6mo, 

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Reed's Engineers' Handbook 8vo, 

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Marine Boilers nmo, 

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Reinhardt, C. W. Lettering for Draftsmen, Engineers, and Students. 

oblong 4to, boards, 

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Reiser, F. Hardening and Tempering of Steel. Trans, by A. Morris and 

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Renwick, W. G. Marble and Marble Working 8vo, 






50 





50 





50 


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00 


2 


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24 D. VAN NOSTRAND CO.'S SHORT TITLE CATALOG 

Reynolds, 0., and Idell, F. E. Triple Expansion Engines. (Science 

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Rhodes, H. J. Art of Lithography 8vo, 3 50 

Rice, J. M., and Johnson, W. W. A New Method of Obtaining the Differ- 
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Richards, W. A., and North, H. B. Manual of Cement Testing. . . . i2mo, *i 50 

Richardson, J. The Modern Steam Engine 8vo, *3 50 

Richardson, S. S. Magnetism and Electricity nmo, *2 00 

Rideal, S. Glue and Glue Testing 8vo, *4 00 

Rimmer, E. J. Boiler Explosions, Collapses and Mishaps 8vo, *i 75 

Rings, F. Concrete in Theory and Practice nmo, *2 50 

Reinforced Concrete Bridges 4to, *5 00 

Ripper, W. Course of Instruction in Machine Drawing folio, *6 00 

Roberts, F. C. Figure of the Earth. (Science Series No. 79.) i6mo, o 50 

Roberts, J., Jr. Laboratory Work in Electrical Engineering 8vo, *2 00 

Robertson, L. S. Water-tube Boilers 8vo, 2 00 

Robinson, J. B. Architectural Composition 8vo, *2 50 

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Rogers, A. A Laboratory Guide of Industrial Chemistry i2mo, *i 50 

Rogers, A., and Aubert, A. B. Industrial Chemistry 8vo, *5 00 

Rogers, F. Magnetism of Iron Vessels. (Science Series No. 30.) . i6mo, o 5o 
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W. J. Britland and H. E. Potts 12010, *i 25 

Rollins, W. Notes on X-Light Svo, *5 oa 

Rollinson, C. Alphabets Oblong, i2mo, *i 00 

Rose, J. The Pattern-makers' Assistant 8vo, 2 50 

Key to Engines and Engine-running nmo, 2 50 

Rose, T. K. The Precious Metals. (Westminster Series.) 8vo, *2 00 

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Roth. Physical Chemistry 8vo, *2 00 

Rouillion, L. The Economics of Manual Training 8vo, 2 00 

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Roxburgh, W. General Foundry Practice. (Westminster Series.) .8vo, *2 co 
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Russell, A. Theory of Electric Cables and Networks 8vo, 

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*3 


50 


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Scheele, C. W. Chemical Essays 8vo, *2 00 

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Schellen, H. Magneto-electric and Dynamo-electric Machines. . . . 8vo, 5 oa 

Scherer, R. Casein. Trans, by C. Salter ># 8vo, *3 00 

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Seaton, A. E., and Rounthwaite, H. M. Pocket-book of Marine Engi- 
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Gutta Percha. Trans, by J. G. Mcintosh 8vo, *5 00 

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Shaw, Henry S. H. Mechanical Integrators. Science Series No. 83. I 

:6mo, 

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